Note: this post is a (minorly) edited version of a new 80,000 Hours problem profile.

Summary

History is littered with moral mistakes — things that once were common, but we now consider clearly morally wrong, for example: human sacrifice, gladiatorial combat, public executions, witch hunts, and slavery.

In my opinion, there’s one clear candidate for the biggest moral mistake that humanity is currently making: factory farming.

The rough argument is:

There are trillions of farmed animals, making the scale of the potential problem so large that it’s hard to intuitively grasp.
The vast majority (we estimate 97.5%)^[1] of farmed animals are in factory farms. The conditions in these farms are far worse than most people realise.
Even if nonhuman animals don’t morally matter as much as humans, there’s good evidence that they are conscious and that they feel pain — and, as a result, the poor conditions in factory farms are likely causing animals to experience severe suffering.

What’s more, we think that this problem is highly neglected and that there are clear ways to make progress — which makes factory farming a highly pressing problem overall.

Scale

We kill around 1.6 to 4.5 trillion animals a year. There’s no consensus about how to compare this to the scale of issues that affect humans, because people disagree about the moral significance of animals. However, we believe there are good reasons to think that the suffering of animals on farms has moral significance. And, just thinking about the suffering involved in the slaughter process, when we adjust for the best quantitative assessment we can find for how 1.6 to 4.5 trillion animals being killed per year compares to human suffering, this amounts to the equivalent of around 60 million to 800 billion humans going through that same experience. (Though this is a very under-researched question, so this conversion should be treated as extremely uncertain – see below.)

This is also just a rough proxy for the scale of the issue; before slaughter, these animals are almost always kept in factory farming conditions, where we’d guess they suffer great harms. As for the future, we expect this problem to worsen in the short term but we would guess that working on it doesn’t have a substantial impact on the very long-term future.

Neglectedness

This issue is highly neglected. We’d estimate there are approximately 3,000 people working on reducing harms from factory farming and around $400 million dedicated to this issue.

Solvability

This seems moderately tractable and there are some plausible ways we could make progress.

Introduction

We’re going to start by investigating how important we should consider ending factory farming to be — that is, how much good would be done if we solved the entire problem.

We’ll look at:

How many animals are in farms and how we treat these animals
The extent to which animals deserve our moral consideration, according to various moral theories
How factory farming is likely to change in the future, as the quantity and quality of life of future factory farmed animals are also part of assessing the importance of the problem
How we can compare factory farming with existential risks, which are the main category of other problems we consider most pressing

We’ll then look at whether there are ways to make progress and how neglected factory farming is before discussing how you can help solve this problem with your career.

How many animals are in farms?

Every year, we kill somewhere between 400 billion and 3 trillion vertebrates (e.g. cows, chickens, fish) — some are killed for sport and some are dissected for experiments, but the vast majority are either slaughtered for food or die in farms before they’re old enough to be purposefully slaughtered.^[2]

That doesn’t mean there are trillions of animals in farms at any given time, as the lifespan of these animals is often less than a year. There are probably around 120–210 billion vertebrates alive in farms at any given time.^[3]

If we include invertebrates (e.g. octopuses, insects, crabs, snails, shrimp) — which is more controversial because we have less evidence of their ability to feel pain — it’s more like 1.6–4.5 trillion farmed animals killed per year, and around 350–700 billion animals alive in farms at any given time.

It’s much harder to estimate how many of these animals are in factory farms. In part, this is because ‘factory farming’ doesn’t have a clear definition. Generally, we’d say something is a factory farm if it has generally poor welfare conditions and a large number of animals in a small space (‘high stocking density’).

Rather than drawing a clear distinction, we’ll go through how different animals tend to be treated on farms and note any key variations, such as in standards between countries^[4] or what it means for hens to be ‘cage free.’

We don’t to focus on animals that aren’t farmed — wild animal welfare and animals killed by fishing and hunting are whole separate issues.^[5]

This table shows some estimates for various species. For vertebrates, we’ve only included species where we farm more than 100 million animals at any one time (so, for example, frogs and turtles but not snakes or salamanders). We’ve included data for all vertebrate species we could find – we farm many other invertebrates, like cephalopods (e.g. squid), and bivalves (e.g. clams, oysters), but we couldn’t find any good estimates of how many of these animals are in farms.

Farmed animal	Alive in farms at any one time	Slaughtered per year
Chickens	24 billion (10 billion broilers – chickens bred for meat; 7–10 billion egg-laying hens)	72–77 billion (69 billion for meat; 3-9 billion male chicks from the egg industry)
Pigs	1 billion	1.5 billion
Cattle (cows)	1.5 billion	0.3 billion
Sheep and goats	2.2 billion	1 billion
Ducks	1 billion	3 billion
Quail	0.5 billion	1.5–2.5 billion
Turkeys	0.5 billion	0.7 billion
Geese and guinea fowls	0.4 billion	0.7 billion
Fish	100–180 billion	100 billion
Frogs	0.1–2.6 billion	0.3–1 billion
Chinese softshell turtles	0.3–2.1 billion	0.2–0.9 billion
Crabs	--	5–15 billion
Crayfish and lobsters	--	40–60 billion
Shrimp	--	210–530 billion
Snails	--	3–8 billion
Crickets	35–40 billion	370–430 billion
Mealworms	25–30 billion	290–310 billion
Black soldier files	8–16 billion	190–300 billion

How do we treat these animals?

Let’s go through some of the most commonly farmed animals and look at how they’re treated.

In general, the main issues seem to be:

Poor methods for pre-slaughter stunning, and for slaughter itself
Extremely crowded and dirty living conditions
High rates of disease and injury
Particularly poor conditions during transport
Occasional withdrawals of food and water for extended periods
High rates of painful procedures, often carried out without anaesthetic

We think it’s important to be sceptical of many of the claims of animal advocates — like anyone advocating for a cause, they have incentives to exaggerate their claims. So we’ve relied as much as possible on academic, industry, and government sources, and given extensive detail in the footnotes. We tried hard not to cherry-pick the worst cases of animal abuse — this just reflects how the vast majority of animals are treated.

We’ve carefully selected photographs of what we think represent ‘normal’ farms. Photographs of factory farms can be disturbing, so we’ve haven’t included them in this post. Instead, you can find the photographs in the version of this article on our website.

Farmed chickens

We’ve genetically selected broiler chickens to grow very fast; they may reach the weight for slaughter in as little as five weeks.^[6] This fast development causes fluid to build up in the abdomen, which compresses organs, causing pain and breathing difficulties. This build-up of fluid is known as ascites.^[7] These chickens’ large sizes also cause difficulty moving. Much like injured humans, chickens change the way they move in response to their weight and injury — which then causes muscle and bone pain.^[8]

Their movement is also very restricted, and even on free-range farms each bird often has only around 0.1m² of space.^[9] Long periods of standing and lying in waste causes painful lesions and chemical burns (specifically, ‘hock burn’ and ‘footpad dermatitis’).^[10] Heat stress is common due to temperatures of 30 to 40°C in housing.^[11]

Diseases are common. One of the most common is necrotic enteritis (a bacterial infection that destroys the small intestine over the course of about 3–4 days).^[12] In developing countries, infectious diseases like visceral gout (kidney failure leading to poor appetite and uric acid build up on organs), coccidiosis (parasitic disease causing diarrhoea and vomiting), and colibacillosis (E. coli infection) are common.^[13]

Breeder chickens can live for up to a year, but because they’re still broiler chickens, they’re bred to want to eat a lot. Feeding breeders isn’t that helpful for farmers (in fact, it can lead to injury, health issues, and fewer chicks being born), so instead they are kept on the edge of starvation.^[14]

Before slaughter, chickens must be ‘caught’ and loaded into trucks for transport. This process involves humans or a machine picking up and loading chickens into crates. Often, this is done to half the flock, while the rest are left without food or water for days until they are also collected. This process is known as ‘depopulation.’^[15]

In some systems, like those in Europe, 90% of chickens are stunned before slaughter,^[16] mostly by having their heads dunked in water with an electric current. In other countries, like the US, there are no rules governing how chickens are killed.^[17] Many chickens experience severe pain when they are shackled upside down by their legs prior to stunning.^[18] Chickens then have their throats cut (‘bleeding’), before being killed using hot water — as a result, many chickens are boiled alive when the previous steps fail.^[19]

Caged laying hens tend to have around 0.07 m² of space, which prevents typical movement and behaviours, including standing, preening, turning, and wing flapping, and prevents them from engaging in natural behaviours like nesting or foraging.^[20] Osteoporosis leads to frequent fractures of the keel bone (the part of the sternum where the wings attach).^[21] Withdrawal of food and exposure to 24-hour bright lights is sometimes used to induce shedding and regrowth of feathers (known as moulting) to increase egg production in countries outside of Europe.^[22] Egg peritonitis — an infection caused by yolks remaining within their body cavity from eggs that break before they are laid — is quite common, causes substantial pain, and is sometimes fatal.^[23]

The lives of cage-free hens are marginally better. They are usually kept in indoor aviaries, and free-range hens go outside less than consumers expect.^[24] Cage-free hens have a little more space per bird, and are able to move around somewhat. Keel bone fractures are still common.^[25]

However, because of stress and the inability to socialise naturally with such a large flock, hens still end up wounding each other by pecking and sometimes even resort to cannibalism.^[26] As a result, it’s common to remove the tip of both caged and cage-free hens’ beaks using a hot blade, without anaesthesia. Beaks are highly sensitive and used by birds to interact with the world, similar to how humans use their hands.^[27] Male chicks are killed by maceration.^[28] Egg-laying hens are depopulated and slaughtered when they are old enough that their productivity drops, with similar issues to the slaughter or broiler chickens.^[29]

Other birds (ducks, quail, turkeys, gueese, guinea fowls) are treated very similarly to chickens).

Farmed pigs

Most farmed pigs are kept indoors on high-density farms.^[30] Heat stress is common, reaching temperatures of 30 to 40°C — which is particularly bad as pigs do not sweat; instead they keep cool in the wild through wallowing and rooting.^[31]

Piglets go through the removal of parts of their canine teeth (known as tooth cutting)^[32] and their tails (known as tail docking)^[33] without anaesthesia. Most male piglets are also castrated (other than in the UK and some EU countries) to prevent the strong odour and taste of meat associated with uncastrated pigs (known as ‘boar taint’).^[34]

A small proportion of pigs are kept outdoors. However, these pigs usually have metal or wire rings inserted into their noses (nose ringing), which deliberately causes pain when pigs go to root in order to prevent the ground from being upturned.^[35]

The worst conditions are experienced by breeding sows. In countries other than Sweden and the UK, pregnant sows are kept in gestation crates — small pens so narrow that they cannot move or even turn around.^[36] And in countries other than Sweden, Norway, and Switzerland, farrowing crates are used after birth to prevent sows being able to move away from their piglets.^[37] Piglets are weaned at around 3–4 weeks, after which sows are inseminated again immediately, leaving them little time outside of these small pens.^[38]

At slaughter, pigs undergo electric stunning, controlled atmosphere stunning (gassing with carbon dioxide), or are not stunned for shackling (i.e. live-shackle slaughter), after which the major arteries near the heart are severed.^[39]

Farmed cattle

Generally, cattle are treated better than chickens and pigs, with 5–10 m² of space per cattle.^[40]

The main issues are:

Many dairy cows are kept in cubicle housing or tie-in stalls (where they are tethered to the stall by their neck) with limited access to pasture for half of the year.^[41] Beef cattle are often ‘feedlot-finished,’ meaning they are kept indoors for 100 to 600 days to increase weight gain.^[42]
Calves have their early horns (known as “‘buds’”) removed by having their heads burned with a hot iron, or through chemical burns, often without anaesthesia. Older cattle sometimes go through a much more painful process where their grown horns are removed using tools like shears or saws.^[43]
Lameness (damage or weakness to limbs) and mastitis (inflammation of the udder) are common causes of pain in dairy cows.^[44] Indoor floors for beef cattle usually have gaps in them to allow excrement to fall through, but this makes injury much more common.^[45]
Dairy cows are kept pregnant to ensure constant milk production. This creates an issue: dealing with the unwanted calves. All male calves and almost all female calves are separated from their mothers pretty much immediately — both calves and mothers appear to cry for each other for days to weeks afterwards.^[46]
Male calves from the dairy industry are often killed shortly after they’re born.^[47] This is because dairy cows and meat cows are different breeds bred for different traits. If they are kept for meat, it’s usually veal. Veal calves are fed an iron-restricted diet to keep their flesh pale. Outside the EU, veal calves are usually raised in single-occupancy crates no bigger than the calves: these prevent almost all socialisation and movement for some or all of their (short) lives.^[48]
Transportation to the slaughterhouse is stressful, with cattle spending long periods in cramped conditions without food or water. Dairy cows that are no longer producing milk at a profitable rate usually have some kind of injury or disease, making it harder to deal with these sorts of conditions.^[49]
At slaughter, the use of electric goads causes pain, and there are poor conditions in the resting areas at slaughterhouses. Cattle are usually stunned with a bolt gun or electric shock, which often fails, leaving cattle conscious when they are hung upside down by one leg while their throats are cut and their trachea removed. Throat-cutting sometimes intentionally occurs without stunning.^[50]

Farmed sheep and goats

Sheep and goats also tend to be treated better than chickens and pigs, and are largely kept in extensive farms.

The main issues are:

Both sheep and goats are castrated. The usual method is by tying an elastic ring around the scrotum, restricting blood flow while the scrotum gradually dies and then falls off. In sheep, the same is also done to their tails, which take 4–6 weeks to fall off. This is often done without anaesthesia.^[51]
Goats have their early horns (known as ‘buds’) removed by having their heads burned with a hot iron, often without anaesthesia.^[52]
Lameness (damage or weakness to limbs) is a common cause of pain. In sheep, this is often caused by bacterial infections known as foot rot and foot scald.^[53]
Mastitis (inflammation of the udder) is relatively rare in sheep and goats kept for milk production, but can be very painful.^[54]
Around 15–20% of lambs die on farms before slaughter — for example, from disease, extreme hot or cold temperatures, or starvation. Around half of these die soon after birth, often because of complications resulting from the birth itself.^[55]
Lambs are separated from their mothers well before they would naturally leave, which has a clear behavioural (and likely emotional) effect on both lambs and their mothers.^[56]
Transport to slaughter is often in overcrowded trucks without food or water. When trucks are stationary in hot weather, sheep and goats experience extreme heat.^[57]
While waiting for slaughter, sheep and goats are in cramped conditions with limited access to food and water. They are stunned with a blow to the head or by electrocuting their heads, although not all sheep and goats are stunned successfully — and some are not stunned at all.^[58]

Farmed fish

We’re more uncertain about what produces a poor welfare environment for fish, and there are so many different species of fish that it’s difficult to say much about their welfare in general. For example, it seems like some fish prefer high stocking density environments. (There are a variety of reasons for this, including that high stocking density can prevent territorial and aggressive behaviour).^[59] Other fish species seem to prefer more turbid (murky, dirty-looking) water to clean water.^[60]

That said, there are almost no legal protections for fish welfare.^[61] Somewhere between 15 billion and one trillion fish die in farms before reaching slaughter age,^[62] and that high pre-slaughter mortality rate is a bad sign for their general welfare.

Common issues in fish farms include:

Poor water quality, including insufficient dissolved oxygen; inappropriate temperature, pH, and salinity; and build ups of ammonia and nitrates from waste^[63]
Disease and parasites,^[64] such as sea lice^[65]
Other stressors related to the harsh environment — like withdrawal of feed — which lead to injury (e.g. fin erosion),^[66] and cannibalism^[67]

Since fish are smaller than most land-based farm animals, more fish are killed for the same amount of food. What’s more, unlike herbivorous land-based farm animals, predatory fish such as tuna and salmon (and the lesser-known mandarin fish)^[68] must be fed other fish, which are often still alive, increasing the welfare concerns per animal sold.

Many issues occur at slaughter. Common slaughter methods include:^[69]

Leaving fish in air to slowly suffocate to death over the course of several minutes^[70]
Putting fish in baths of ice slurry where they gradually lose consciousnes. In theory, fish are left until they die from lack of oxygen before they’re cut open and drained of blood. But sometimes, if fish aren’t left in the ice slurry long enough, or if there isn’t the right ratio of ice to water and fish, they can recover and regain brain function as they warm up, leaving them conscious when they’re cut open.^[71]
Bubbling carbon dioxide into the fish’s water to make it gradually acidic, which eventually stuns the. Fish will swim vigorously and try to escape the tank when this is done. Again, if fish are removed too early or the water doesn’t become acidic enough, they’ll be conscious when they are cut open.^[72]
Simply cutting off the gills of a fish, causing them to bleed out and suffocate to death^[73]

Farmed frogs and turtles

Frogs and turtles are kept at such high density that they must stand on top of each other to have enough space. Tadpoles and froglets have extremely high rates of disease — in particular, septicemia, which can frequently cause swelling of the whole body and for the stomach to hang out of the frog’s mouth, as well as convulsions, paralysis, and death. Farmed Chinese softshell turtles have high rates of white-spot disease, which causes skin lesions, lack of eating, and eventually death.^[74]

Frogs are stunned by being left in an ice bath for around 15 minutes or by being given a few-second-long electric shock, after which they are cut open — but we’re unsure about compliance or success rates. We’re unsure how Chinese softshell turtles are slaughtered, but it’s claimed that turtles are often beheaded or have their shells removed without stunning.^[75]

Farmed shrimp and crustaceans

The main welfare issues for shrimp (the vast majority of farmed decapod crustaceans) are:^[76]

Poor water quality — which could include a lack of oxygen to breathe, or swimming around in their own waste
Disease — symptoms include spots, lethargy, body deformities, changes in colour, reduced food intake, and death
Eyestalk ablation — blinding shrimp by removing one or both of their eyestalks, usually by pinching, cutting, or burning them off
Slaughter — by being left in the air to suffocate or being crushed by other shrimp

Crustaceans more broadly are routinely boiled alive just before being eaten — and therefore travel extremely long distances while alive.

Other farmed invertebrates (snails and insects)

We’re very uncertain about what produces a poor welfare environment for these animals.

Welfare concerns for snails appear to include: high stocking densities, disease, purging (starvation before transport to ensure there’s no undigested food left inside when they’re eaten), live transport, and slaughter by boiling alive.^[77]

The main welfare concerns for insects (including black soldier flies, mealworms, and crickets) include: high stocking densities,^[78] disease and parasites,^[79] cannibalism,^[80] injury,^[81] handling stress (such as vibrations that may be perceived as predatory attack, or exposing light-averse insects to bright lights),^[82] withdrawal of food before slaughter or from adults (in particular, black soldier fly adults are never fed),^[83] live transport,^[84] and slaughter by roasting, baking, microwaving, freezing in air or asphyxiation — all without anaesthesia.^[85]

To what extent do animals deserve our moral consideration?

On reading the above, it’s pretty clear that if even some animals deserve our moral consideration, something pretty awful is happening. But to what extent some or all animals deserve our moral consideration is, in fact, a subject of substantial debate.

We’re going to look at:

Whether animals are conscious and whether they feel pain
What various ethical theories say about which beings deserve our moral consideration — we’ll consider a wellbeing-based approach, as well as other moral theories
Some quantitative estimates, based on these discussions, of how many animals it’d be reasonable to count morally the equivalent to one human, to help estimate the scale of the moral problem of factory farming

Overall, we find that while there’s disagreement on these issues, and grappling with this moral uncertainty is tricky, there’s generally enough agreement on the science and among plausible moral theories that the correct approach is to give many species of nonhuman animals — including the ones we keep on factory farms — at least some non-negligible moral consideration.

Animal consciousness and pain

Many of the moral arguments we’ll consider below come down to whether animals are conscious and whether they have the capacity to feel pain.

The question of consciousness remains highly philosophical. By consciousness, we mean phenomenal consciousness (or capable of subjective experience) — that is, we mean that there is ‘something it’s like’ to be a certain animal in the same way there’s ‘something it’s like’ for you to experience a sunset or a good mood.

The main ways we get evidence about the consciousness of other humans is by communicating via language and by analogy to our own minds (if you’re conscious, other people probably are too). But we can’t clearly communicate with nonhuman animals, and their minds are less similar to our own, so it’s harder to argue by analogy.

But there is plausibly a way to make progress. By looking at the various philosophical and scientific theories of consciousness, we can try to identify “potentially conscious-indicating features,”^[86] and then look for these features in animals.

A 2017 report by researcher Luke Muehlhauser identified over 40 features which are indicative of consciousness.^[87] They fall into a few categories:

Broad similarity with humans — there are, of course, many ways to measure this. Following Muehlhauser, we’ll look at the time since the closest common ancestor with humans.^[88] The other three categories in this list can also be seen as measures of similarity with humans.
Neurobiological features — in particular, having a large brain and a centralised, complex nervous system.
Clear and complex nociception — the physical states and behaviours associated with feeling pain in humans. For example, having fibres that respond to dangerous stimuli (known as “nociceptors”), protective behaviour like wound guarding or limping, responding to painkillers, and learning to avoid things that cause nociceptors to fire.
Other indicators of cognitive ability — like play behaviour,^[89] grief behaviour, mirror self-recognition, tool use, language capabilities, or theory of mind. While the relationship between cognitive ability and phenomenal consciousness is not well understood, many philosophers and scientists think there’s likely an association between the two.^[90]

So let’s look at some of the animals we keep in factory farms and assess them on some of these criteria.

We’ll pay particular attention to nociception, because it’s both an indicator of consciousness, and also — as we’ll see below — plausibly an indication of these creatures being worthy of moral concern in themselves (that is, that they have ‘moral status’).^[91]

Unfortunately, there’s still a lot we don’t know in this area (even things like how many neurons are in the brains of various animals). So there are lots of gaps in the tables below — even among the small number of indicators we’ve decided to focus on.

	Humans	Chickens	Pigs	Fish	Insects
Time since closest ancestor with humans^[88]	N/A	310 million years ago	95 million years ago	400 million years ago (lungfish) to 530 million years ago (jawless fish)	700 million years ago
Brain and nervous system	Avg. adult brain mass: 1300g^[92] Neurons in brain: 85 billion^[93] Have a neocortex and a central nervous system	Avg. adult brain mass: 3.5g^[94] Neurons in brain: 220 million^[95] May have a neocortex-like structure^[96] and have a central nervous system	Avg. adult brain mass: 135g^[97] Neurons in the brain: 430 million^[98] Have a neocortex^[99] and a central nervous system	Avg. adult brain mass: 0.2g (rainbow trout), 0.3g (carp), 1g (salmon)^[100] Total number of neurons: 10 million (zebrafish)^[101] Don’t have a neocortex,^[102] but do have a central nervous system	Avg. adult brain mass: 3mg (bees), 1.6mg (Apoidea), 0.6mg (black soldier flies), 0.4 to 0.06mg (butterflies)^[103] Total number of neurons: 600,000 (western honey bee), 300,000 (black soldier fly), 100,000 (fruit fly)^[104] Have a central nervous system but nothing clearly resembling a neocortex
Nociception^[105]	Neural nociceptors and reflexes to move away from dangerous stimuli Nociceptors respond to painkillers Self-administer painkillers if needed (and even pay a cost to do so) Exhibit protective behaviour (e.g. wound guarding, limping)	Neural nociceptors^[106] and reflexes to move away from dangerous stimuli^[107] Nociceptors respond to painkillers Self-administer painkillers if needed (no studies were found on whether they would pay a cost to do so).^[108] Exhibit protective behaviour^[109]	Have neural nociceptors^[110] and reflexes to move away from dangerous stimuli^[111] Nociceptors respond to painkillers,^[112] but no studies were found on self-administration Exhibit protective behaviour.^[113]	Have neural nociceptors and reflexes to move away from dangerous stimuli^[114] Nociceptors respond to painkillers. They may self-administer painkillers if needed (and pay a cost to do so), but the evidence is unclear (zebrafish)^[115] Exhibit protective behaviour (carp, zebrafish, rainbow trout)^[116]	Have neural nociceptors, and reflexes to move away from dangerous stimuli Nociceptors respond to painkillers^[117] Exhibit protective behaviour (bumblebees)^[118]
Other indicators of cognitive ability^[105]	Play behaviours and grief behaviours Clear tool use Recognise themselves in mirrors^[119] Can move around obstacles to reach a goal (even when they temporarily can’t sense the goal)^[120] A range of other cognitive abilities not observed in other animals which people have argued indicate consciousness, such as abstract language capabilities and the ability to do mental time travel	Play behaviours^[121] Grief behaviours have been claimed by some backyard chicken owners,^[122] but we found no studies confirming this No clear tool use^[123] Might recognise themselves in mirrors (although don’t pass the conventional mirror test)^[124] Can move around obstacles to reach a goal (even when they temporarily can’t sense the goal)^[125]	Play behaviours,^[126] and likely experience grief (but we’re not sure)^[127] Tool use^[128] Do not pass the mirror test^[129] Can move around obstacles to reach a goal (even when they temporarily can’t sense the goal)^[130]	Likely play behaviours,^[131] but no clear grief behaviours Tool use (wrasse, cichlids, whitetail majors)^[132] Cleaner wrasse pass the mirror test^[133] Can move around obstacles to reach a goal (even when they temporarily can’t sense the goal) (zebrafish, goldfish)^[134]	Most indicators have not been studied Some complex behaviours have been found, including: - moving around objects in complex ways (bees)^[135] - pessimism (bees)^[136] - learned helplessness and response to antidepressants (fruit flies)^[137] - something a bit like tool use or play behaviour (bees)^[138] - anxious-avoidant behaviour which responds to anti-anxiety drugs (fruit flies)^[139]

Each indicator that’s present for a species is some evidence for its consciousness; similarly, each indicator that’s missing is some evidence against.

But it’s not really clear how much evidence each indicator provides — without a decisive underlying theory, there’s no obvious way to interpret the data. And this table is notably incomplete, so much so that evidence not included is probably more significant than the evidence presented!

We know of two other surveys of the evidence that look at many more possible indicators and a wider variety of species,^[140] but these are also still very incomplete.

There are other issues with these indicators:^[141]

Many systems typically thought to be non-conscious (for example the spinal cord, plants, bacteria, and some computer programs) have at least some of the above features.
Many of the behaviours discussed can also occur unconsciously in humans, which suggests they’re not great evidence for consciousness.^[142]
And lots of the information might be mistaken — much of this is based on single studies, many of which may fail to replicate.

That said, if you’re anything like me, you probably find the extent to which animals express complex behaviours pretty surprising — which suggests that we should be more confident they are conscious. In fact, it seems like we are generally finding, over time, that sophisticated behaviours are more common than we once thought.

There may be other ways of making progress on whether animals are conscious, but we haven’t found any to be particularly illuminating.^[143]

Overall, there are three takeaways we feel pretty confident in:

It seems very hard to rule out that the animals we keep on farms are conscious.
It seems even harder to rule out the existence of nociception in these species.
The evidence varies from species to species, and seems stronger for animals like pigs and chickens than for fish or insects.

It seems to us that, given the evidence we currently have and the huge uncertainty, it’s hard to justify thinking that the probability of consciousness for any factory farmed animal is less than, say, 5%. And for some animals (chickens, sheep, goats, cows, pigs), I think the chances of consciousness seem above 80%.

What makes something deserving of moral consideration?

So, if some species of animals are conscious and have nociceptors (pain responses) or emotion, what does that imply about their moral status?

We’ve argued previously that a core aspect of doing good is about promoting wellbeing, considered impartially. In short, this is because when it comes down to it, most moral theories agree that:

If you can make others better off — i.e. increase wellbeing — that’s a good thing to do.
It’s even better to make more individuals better off than fewer.
This is true equally, no matter who those individuals are (as long as, and to the extent that, they are capable of wellbeing).

(Read about this argument in more detail.)

So we can then consider whether each species has something that constitutes ‘wellbeing.’

There are three broad theories of wellbeing:

The hedonistic view, where what matters is the degree of positive vs negative experienced mental states (e.g. happiness vs pain)
The preference satisfaction view, where wellbeing means getting what you (perhaps most deeply) want
Objective list theories, where wellbeing consists of achieving things on a ‘list’ of objectively good states or events, e.g. friendship, knowledge, happiness, love, virtue, wisdom, and health

Overall, the hedonistic view appears to place the most confidence in animals having the capacity for wellbeing — it seems clear that if an animal is conscious and has pain responses or emotion, then they can have positive or negative experiences.

It’s less obvious that animals have preferences — nailing down exactly what philosophers mean by preferences is really difficult — but that many animals act to avoid pain is at least suggestive of the concept of preferences. (That said, some preference utilitarians argue that preferences require language, e.g. R. G. Frey.)

It’s also very unclear to what extent animals have the capacity for virtue or wisdom — so animals might be missing the capacity for many important items on objective list theories of wellbeing. But in practice, most people (including philosophers of wellbeing) would include ‘lack of pain’ and ‘happiness or pleasure’ as important goods to obtain on any ‘objective list.’

This suggests that on every mainstream view, there’s an argument that animals are capable of wellbeing, though it’s especially clear in the hedonistic case.

There’s lots more to discuss here, and many more objections and counter-objections to consider. For a more in-depth discussion, we’d recommend Comparisons of Capacity for Welfare and Moral Status Across Species by Jason Shukraft.

Different moral approaches

Many people believe some version of ‘welfarism’ — the view that the welfare of individuals is in fact the only source of moral value.

If welfarism is right, the above analysis suggests that animals do deserve our moral consideration, since they seem likely to be conscious and to be capable of welfare and suffering.

There are good arguments for welfarism, but we think it makes sense not to be too confident in any particular moral theory — so it’s worth considering what other views have to say about the moral standing of animals.

Do any other popular theories suggest that, even if factory farming is large in scale, solvable and neglected, we should nevertheless not consider it to be a particularly pressing problem because animals shouldn’t be given much (or any) moral consideration?

There is too much here to give a comprehensive overview, but here are short descriptions of some of the most well-known theories and what they have to say about animals:

Kantian personhood. Kant argues that fundamental moral value comes from being a rational being — and that only humans meet his criteria for being rational. In recent years, philosopher Christine Korsgaard has developed this idea into the claim that humans face a unique “problem of normativity” as a result of our ability to think about our desires. One common critique of this approach is the problem of “marginal cases”: many humans, like babies and people in comas, don’t have the capacity for rationality or self-reflection in the sense required by Kant and Korsgaard, but do seem to deserve moral consideration. Korsgaard rejects this critique, but nevertheless concludes that animals should be treated as “ends in themselves” under a Kantian view of ethics. (Read more on Kantian personhood.)
Contractarianism similarly only grants moral status to rational agents that can comprehend the idea of a social contract. Mark Rowlands argues that some forms of contractarianism do grant status to animals, because behind a veil of ignorance (where the moral choice is the one you would make if you didn’t know your ethnicity, gender, social status, or species), one would support the moral consideration of animals. That said, it’s common to interpret contractarianism as excluding animals from moral concern because in a thought experiment of forming a social contract, they’re not sophisticated enough to participate. However, one prominent defender of a related view, T. M. Scanlon, notes that his version of contractualism only accounts for one domain of morality (what we owe to other people) — which doesn’t rule out that other domains (such as obligations with regard to the environment) could include moral reasons to respect the interests of animals.
Rights-based approaches. Many philosophers have argued for and against the concept of animal rights. Tom Regan argues that all mammals of at least one year in age have rights, because they have certain cognitive abilities like perception, memory, sense of the future, and capacity for pain. Gary Francione argues that animals have the right not to be owned, and that just that one right is sufficient for a huge change to our practices. Carl Cohen – a critic of rights-based approaches to animal rights — argues that rights-holders must have the capacity to comprehend ‘rules of duty’. It’s also common to think that rights are an important part of morality and that protecting the welfare of individuals is good too, even if it’s separate, or less important. So a rights-based approach seems to not lean clearly one way or another.
Capabilities approach. This approach, developed by Martha Nussbaum and Amartya Sen, suggests that a just society arises if people are given the chance to flourish and achieve things like health, safety, and social relationships. Nussbaum argues that this approach requires us to also let animals achieve, at the very least, a lack of suffering. (Read more in her book, Justice for Animals.)
Virtue ethics. Virtue ethics approaches tend to think that compassion and care, including for animals, are virtues, but disagree on the extent to which this implies actions like refraining from factory farming.
Even if animals have moral standing, there are views of what it means for some state of the world to be better than another that might suggest that factory farming isn’t such a pressing concern — in particular, person-affecting views. These views argue that we only have moral obligations to help those who are already alive, not to enable more people or other beings to exist with good lives. Since the vast majority of animals on farms live very short lives (usually less than a year), most of the problem of factory farming arises with regard to the treatment of animals who aren’t yet born. As a result, even if we do give moral consideration to animals, the scale of the problem is substantially reduced under these person affecting views, which would make it much less pressing overall. That said, philosophers who defend person affecting views often think there’s an asymmetry where, while it’s not good to bring someone with a good life into existence, it is bad to bring someone into existence just to suffer. If that’s right, the problem of factory likely remains very large. (Read more about person-affecting views).
Finally, many “common sense” approaches to ethics suggest that many of the standard industry practices in factory farming (described above) are wrong, even if they don’t have a considered view about animals’ moral standing.

So it’s not the case that no matter what your view of morality, factory farming is an especially pressing issue. However, most moral theories seem to put at least some weight on animals (often as a result of their consciousness and capacity to feel pain, and sometimes as a result of apparent preferences or capacity for flourishing). Since we’re philosophically uncertain about the nature of morality or the moral standing of animals, we don’t think we can rule out the basic argument above that animals do have moral standing, making factory farming a large-scale problem.

You also don’t need to treat every moral theory as having a vote in your deliberation — an alternative approach to moral uncertainty is to think about how confident you are in a given moral theory and think about the expected choiceworthiness of an action.

For us, both approaches point to giving at least some non-negligible moral weight to animals, and plausibly quite a lot — though your views could be sufficiently different that you disagree.

How many animals count morally the same as one human?

Even if animals deserve our moral consideration, it doesn’t mean that we should count animals the same way we count humans.

Counting the number of individuals

Counting the number of people affected is usually important for how we compare the effects of actions that only affect humans — an action that affects two humans is considered twice as important as one that affects only one human (all else equal).

If moral status doesn’t have degrees (i.e. something is either worthy of moral consideration or not), a view argued for by philosophers such as Kant, Regan, and Francione, then this sounds like a reasonable way to count animals too, as long as the animals meet the criteria for moral consideration.

However, this leads to some strange conclusions, like an overriding consideration for the welfare of insects because they are so numerous.

It also seems plausible that moral status does come in degrees — in which case we should ask how much moral status each animal has.

Counting the number of neurons

One common way trying to approximate the moral status of different animals is assuming each individual has some fixed capacity for wellbeing in fixed proportion to the number of neurons they have.^[144]

This substantially changes how we compare animals to humans.^[145]

Total population	Neurons per animal	Total neurons across the population
Humans	8 billion	85 billion
Chickens	24 billion	220 million
Pigs	1 billion	430 million
Cows	1.5 billion	6 billion
Farmed fish	100 billion to 180 billion	10 million

While this method is simple, and tempting, we think there are lots of good objections to using solely neuron counts as proxies to moral weight. These objections focus on showing that while neuron count probably does correlate with the amount of moral consideration you should give an animal, these correlations are very imperfect. For example, there are a large number of studies showing that decreased brain volume can increase the intensity of experiences (like chronic pain) in humans.^[146]

As a result, we think we can’t conclude much just from neuron counts, other than that we should probably give somewhat more consideration to humans than to nonhuman animals. The extent of that additional moral consideration remains unclear — and neuron counts seem a poor proxy.

Trying to estimate the probability of consciousness

Rather than just using neuron counts, we can attempt to come up with an estimate of how likely we think each species is to be conscious — and then weigh each individual by that probability.

Ultimately, this is very difficult to do, and we haven’t found any work that does much better than the conclusion we already came to above: that it’s hard to justify thinking that the probability of consciousness for any adult factory farmed animal is less than around 5 percent.^[147]

Using welfare ranges

The most recent and most comprehensive approach to comparing animals to humans was pioneered by Jason Schukraft and Bob Fischer, two philosophers working for Rethink Priorities’ Moral Weight Project.

They try to assess animals’ capacity for welfare, which they split into two components:

Their lifespan — if animals live longer, they will experience more
Their welfare range — how much capacity they have for welfare in each moment

To assess these welfare ranges, Rethink Priorities got together a team of three philosophers, two comparative psychologists, two fish welfare researchers, two entomologists, an animal welfare scientist, and a veterinarian. They listed 82 different possible proxies for welfare ranges (things like animals’ response to painkillers, the mirror test, or finding depression-like behaviour), and investigated them for a range of animals.

Next, they aggregated this information using 12 different assumptions, for example:^[148]

Going by neuron count alone
Using multiple different quantitative measures (such as brain mass to body mass ratio and the maximum number of nociceptor spikes per second), and then taking a weighted average of the ratio between these values and the values in humans
Looking at the proportion of the qualitative proxies each animal has compared to humans (humans have all the proxies)
Looking at just certain subsets of the proxies or using quantitative adjustments that exaggerate the differences between species

Using nine of these assumptions (mainly qualitative assumptions as well as neuron counts), the researchers used a simulation to determine welfare scores, and quantified their uncertainty.^[149]

They then made two adjustments to the models:

The researchers assumed there is a 28% chance that an animal’s subjective experience of time varies by species. That is, perhaps there are more “experienced moments” per second for some species than others, that should increase the welfare range. They tried to estimate this effect.^[150]
The researchers made some guesses about the probability each animal was conscious.

Finally, they combined the results from these nine assumptions.^[151] Here are their results:^[152]

The means and medians are surprisingly high — based on the mean values, chickens have a welfare range only three times smaller than humans, compared to 1,000 times smaller when using the neuron count method. Even insects, like black soldier flies, have only approximately 100 times smaller ranges than humans. (Rethink Priorities have argued that this result shouldn’t be surprising.)

That said, the main thing to take away from this graph is the high uncertainty: the error bars (representing a 90% confidence interval) are huge.^[153] There’s also a lot that’s subjective here. For example, the researchers estimated an approximately 40% chance that salmon are conscious. If you adjusted this to the 5% lower bound on consciousness for adult farmed animals we suggested above, you’d get an almost 10 times lower estimate (note silkworms are juveniles).

There are also some ways in which these could be underestimates of welfare ranges. In particular, the researchers assumed that if they couldn’t find any studies on a particular proxy, the species did not have that trait, effectively penalising less-studied animals.

Overall, we think the main thing we think this work shows is that extremely low welfare ranges (below 1%) are unlikely. So we think it makes sense to conclude that adjusting for animals’ capacity for welfare likely doesn’t change our estimate of the scale of the problem of factory farming as a whole by very much.

Interview: Bob Fischer

Bob Fischer is a senior research manager at Rethink Priorities, an associate professor of philosophy at Texas State University, and the director of the Society for the Study of Ethics and Animals. He discussed his work on Rethink Priorities’ Moral Weight Project on our podcast.

LISTEN→

How might factory farming change in the future?

Here’s a graph of the number of land animals being slaughtered each year:

The number of animals being slaughtered is increasing. This is also true for fish farming:

It seems likely that trends will be similar for shellfish and other invertebrates (there’s a nascent and growing insect farming industry).^[154]

Ultimately, we’d guess this trend is primarily caused by the human population getting bigger and richer, increasing the demand for meat.

The number of animals on factory farms isn’t increasing as much in developed countries. This is probably primarily because their populations aren’t growing as much. It also seems that as income per capita increases, meat consumption per capita also increases — but possibly only up to a point. In a few countries, meat consumption per capita is now falling.^[155] We’re not quite sure why this is, but we’d guess that, in part, as people get rich enough, they start being more willing to do things like change their diets in response to climate, health, or animal welfare concerns.

But overall, it looks like meat consumption — particularly from fish and chickens — is going to continue to substantially increase in the short term.

We think roughly all of this increased demand will be met by factory farming — as opposed to bucolic family farms — since it’s by far the cheapest way to produce meat, and probably the only way to produce meat at the scale being demanded without turning most of the planet into grassland.

This could be changed by regulations. Some countries have passed laws to protect the welfare of some farmed animals — but these are far from universal, are poorly enforced, and usually are only small initial steps.

Looking further ahead, meat consumption might stop rapidly increasing if much of the world becomes wealthy enough that average meat consumption per capita stabilises, and the global population stops increasing — which the UN projects will happen around 2080:^[156]

But if you’re looking that far into the future, all the way to 2080, there are so many things that might change about factory farming by then — not just the number of humans who can buy meat. Society’s values might have changed hugely. There might have been a major catastrophe, like a nuclear war or a major pandemic. And perhaps most importantly, technology might completely change the picture.

How will factory farming be affected by technological advances?

We asked some experts what technological advances might affect factory farming in the future. Here are the main things they mentioned:

Widespread use of in ovo-sexing could mean farmers hatch only female chickens, preventing the culling of male chicks.
R&D in aquaculture and insect farming will likely reduce their costs, increase intensification, and support the expansion of these industries. For example, we might see more productive fish and insect breeds, possibly with worse welfare for many (for the same reasons we see worse welfare for chickens that are more productive breeds).
We may develop uses for factory farming other than food for humans or feed for other animals — for example, farming pigs for organ transplants.
We might use gene-editing of animals to enhance either welfare or productivity (potentially at the expense of welfare).
Increasing use of AI to make management decisions on factory farms could make farms more intensive and lower welfare, or could increase care and health for animals, depending on the details.
We might make big strides in plant-based and cultivated (i.e. lab-grown) meat alternatives — which could displace factory farmed meat if they’re able to compete on the market, meaning fewer animals are farmed.

The two developments that seem most likely to completely change the picture are the development of price, taste, and convenience-competitive alternatives to animal products and the development of transformative AI. We’ll look at each of these in more detail below.

When might we develop really good alternatives to meat?

The development of a really good alternative to meat — one that is competitive with meat on price, taste, and convenience grounds — would be a game changer for factory farming.

We’d guess that, if there were more competetitive alternative products, it would be much easier to convince people to stop eating factory farmed meat — and as a result, to push for increased welfare on farms.^[157]

There are three broad approaches to creating alternatives to animal products:

Plant-based alternatives, made solely using ingredients from plants and fungi
Fermentation methods (also known as acellular agriculture), which use microorganisms to create proteins usually found in animal products
Cultivated meat (also known as cellular agriculture), which produces a product cellularly identical to animal meat through cultivating animal cells directly

Each of these approaches faces major challenges.

Plant-based and fermentation methods face difficult challenges in reaching parity with animal products on taste, texture, and on getting plant-based meat to cook like meat.^[158] Fermentation methods produce individual proteins rather than complete products, but combining these animal proteins that aren’t available in plants with plant-based products may overcome some of these challenges.

Ultimately, we’d guess that as long as there are substantial chemical differences between meat and its alternatives, there will be reasons not to switch. For example, people may have worries about health or chemical additives, or feel put off by differences in what the product looks like, feels like, or how it cooks. This is one reason why people are working on cultivated meat.

A 2020 report by David Humbird into cultured meat sparked controversy with its claims that there are severe technical challenges to growing cultivated meat at scale. Humbird’s arguments include:

The low growth rate of animal cells (especially compared to possible infectious microbial cells) means producers need to take expensive measures to ensure a sterile environment.
It’s difficult to transfer oxygen into, and waste out of, a bioreactor without rupturing animal cells, and this will limit the volume (and thus cost-efficiency) of bioreactors.
Scaling up the industry producing the raw ingredients (amino acids and/or plant protein hydrolysates) will be extremely expensive.

We read the full report, along with some responses to it (by the Good Food Institute and by Rethink Priorities) — and ultimately were reasonably convinced that these challenges are real.

That doesn’t mean that cultivated meat is a doomed project — it just means that without something radically changing (e.g. technological progress substantially speeding up in general), it might take a long time until we can use a competitive meat alternative to end factory farming.

Would a competitive meat alternative end factory farming, and if so — when?

There’s more to consider than just the technology. If we have the technology for products that are competitive with meat on their price, taste, and convenience, would that lead to the end of factory farming? If so, how long would that take?

It’s pretty unclear.

First, it’s important to remember that making a real dent in meat consumption requires building up new infrastructure. We currently consume around 1 million tons of meat every single day. Building up a replacement for that would be a gigantic project. Humbird estimates that it would cost hundreds of millions of dollars to build a facility to replace less than 0.01% of the world’s meat.^[159]

There are also lots of other factors that might affect whether people will switch, like social norms, familiarity, food safety, and religion.^[160] These factors are much harder to predict — for example, it’s possible that the development of alternatives to animal products causes political polarisation and worse animal policy overall (although we’d guess that’s less likely than the opposite).

So, what does all this mean for the future of meat production?

It’s pretty hard to bring this information together into a meaningful prediction. We’ve seen two attempts to do this.

On Metaculus, a forecasting website, the aggregate of 268 predictions suggests there’s a 12% chance of a 50% decline in global meat production by 2040.

Rethink Priorities brought together a panel of forecasters to predict how likely it is we’ll have specifically cultivated meat by 2051. Aggregating their estimates suggests that, while there’s an around 50% chance of us producing over 100,000 tons per year by then, there’s more like a 9% chance of us producing over 50 million tons per year. (For comparison, we produced around 350 million tons of meat in 2022.)

But forecasting is really difficult when there are no clearly similar events to point to and when you’re trying to predict low-probability events far into the future, so it’s not clear what we should take away from this.

Perhaps more importantly, the estimates from Rethink Priorities were made assuming that there won’t be some kind of transformative AI (and we’d guess that transformative AI wasn’t much on the minds of the Metaculus forecasters either). And AI could massively change the picture.

How could AI affect factory farming?

As we’ve argued, we think there’s a decent chance that we’ll develop AI systems that are hugely transformative for society within the next few decades.

We think there’s some chance that we could lose control of AI systems. But there’s also a good chance we don’t, and that developers are able to make AI systems that reliably do what their controllers want. If that’s the case, even fairly autonomous AI systems will do roughly what humans want them to do — and so the way any AI system treats animals will be guided by the users’ incentives, beliefs, and attitudes towards animals.

We’ll probably find ways of using AI to make factory farming more efficient through the use of precision livestock farming — we’d guess this is negative overall (because it might lead to increased stocking densities, and it would reduce the price of meat, making it harder for alternative products to compete). But there could be positives too, such as reducing rates of disease. Animal advocates might be able to use AI systems to analyse CCTV footage from slaughterhouses to identify and prosecute violations. (For more on how AI might affect animals in the short term, see this article from Max Taylor, a researcher at Animal Charity Evaluators.)

We’ll likely see these effects just with AI systems that are not too far from the current state of the art.

But how might the development of truly transformative AI — for example, AI systems that can automate a very large proportion of the things that humans can do — affect the picture?

Such systems would have huge economic effects. It’s unclear exactly what these will be, but a simple model is that they would accelerate current economic trends and make society much richer — so we might see an acceleration of the trends we discussed above: per-capita meat consumption rising, peaking, and then declining as wealth increases.

More concretely, if AI systems are able to automate parts of the R&D processes, we’d see an acceleration of all the technological advances discussed above — in particular, the development of price, taste and convenience-competitive alternatives to animal products. As a result, we’d guess it’s highly likely that we’ll develop these alternatives this century.

This wouldn’t necessarily bring the end of factory farming. We’d probably also see technological advances that reduce the price of meat, so there could be a long period of time where meat and alternatives are competing for customers. And as we discussed above, it could take decades to build the necessary infrastructure to replace animal agriculture. And there would still be social barriers preventing the end of factory farming — for example, we could end up in a situation where a large portion of society sticks to traditional meat products for religious reasons.

Overall though, the possibility of transformative AI makes us much more optimistic about the possibility of ending factory farming in the coming century — but it’s by no means a certainty.

What might happen to factory farming in the very long-run future?

We’ve argued before that there are strong reasons to consider the interests of all future generations when assessing the scale of problems — and those arguments apply to future animals, as well as future humans.

That means that, to the extent that we can, we should try to look further ahead than just the coming century.

Here’s a simple sketch of why this matters. If we could end factory farming this century, it would be a fantastic achievement. However, if factory farming were destined to end in the coming centuries anyway, or if factory farming were to reappear, the impact of this achievement would be significantly reduced.

So should we expect factory farming to remain in the long-term future (or reemerge), or not?

Of course we cannot know for sure — or anything close to sure. But there are some long-run factors we can consider to try to come to a provisional view.

One rule of thumb says that we should expect the future to be guided by the values, cultures, and beliefs of people alive today. We’re all in a metaphorical tug of war about the direction of the future, and how society changes over time depends on the winners and losers of that game over the centuries.

It seems like right now things aren’t trending towards an end to factory farming — in fact, factory farming is growing.

Of course, technological changes might affect this: perhaps the real barrier to change is just a lack of alternative products, and today’s society cares enough about animals that it would end factory farming if those were developed.

But current evidence suggests that if a meat alternative was created tomorrow that was competitive on price, taste, and convenience with animal products, many people wouldn’t switch — so if how the future goes is just an extrapolation of what society is like today, we won’t see an end to factory farming.

A different rule of thumb looks to technology and economic efficiency. Ultimately, growing whole animals seems like an inefficient process.^[161] So even if demand for meat remains high, eventually we should expect to develop far cheaper ways of producing meat. Then over time, we might expect people’s values and desires to fall in line with these commercial incentives, and eating animal products will become a weird thing people used to do. Even more radically, perhaps people in the future won’t need food for survival or entertainment — because maybe most people in the future will be digital.

This second line of argument seems more persuasive than the first — which suggests we shouldn’t expect factory farming to last forever.

That said, there’s some chance that society’s values don’t remain malleable, but instead become fixed or put permanently on a particular trajectory at a certain point in time, a possibility known as ‘value lock-in’. It’s been argued that the invention of artificial general intelligence could make it possible to fix the values with which society is governed over very long periods of time.

Ultimately, I think the chances of long-term value lock-in related to animals are very low. It seems that to prevent the drift of values over time, you would need a very controlling system like totalitarianism. We’ve written elsewhere about the chances of a perpetual totalitarian regime and (very roughly) estimated that there’s around a 1 in 330 chance of a stable totalitarian regime arising in the next 100 years. The chances that such a perpetual regime will enforce particular norms about how we treat animals seems even smaller.

So, overall, over the very long-term, we’d guess that factory farming will come to an end.

There are promising ways of solving this problem

As in many areas, the best approaches to solving factory farming are probably hundreds of times more cost effective than others.

Below, we’ll go through a few rules of thumb for finding the best approaches:

Don’t forget about technological advances (especially the plausible development of alternative proteins in the near future).
Find interventions that offer more leverage.
Find interventions that the animal agriculture industry won’t fight.
Don’t cause harm.
Work in neglected areas.

Later, we’ll look at what you could do with your career to help make these happen.

First, we should try to find interventions that take a bet on alternative proteins. As we’ve argued, it seems like factory farming is going to increase over the next few decades unless we develop clear alternatives to animal products. But we think it’s likely that we will develop these price, taste and convenience-competitive alternatives to meat within this century (not least because of the plausibility of transformative AI within the next few decades).

The development of these products in the near future is by no means guaranteed — and competitive products probably won’t solve everything by themselves.

But this means there’s an opportunity: it’ll probably be much easier to reduce meat consumption and improve the lives of the remaining farmed animals once competitive alternatives are developed.

As a result, we think it’s worth taking a bet: interventions whose theories of change assume that alternatives to meat will be developed to a point of market competitiveness seem likely to be more effective overall.

For example, you might work on finding ways to preemptively reduce barriers to the uptake of cultivated meat, such as finding ways to ensure cultivated meat adheres to religious dietary restrictions, or preventing a possible EU-wide ban on cultivated meat (which, if passed, could last decades or more).

Second, we should try to find interventions that offer more leverage — that is, ways of changing how a lot of resources are used, either via knock-on effects or directly.

One great example of this is corporate campaigns. These campaigns try to convince companies to commit to using higher-welfare animal products. Many companies will agree to make commitments without any public campaign, but if they don’t, a campaign might include protests, negative advertising, and criticism on social media. These campaigns are a cost-effective way of helping improve the welfare of large numbers of farmed animals, as they’re fairly cheap to run and can affect the entire supply chain of a large company.

These campaigns have been surprisingly successful. For example, companies such as Burger King, Unilever, and Chipotle have agreed to the Better Chicken Commitment, switching to higher-welfare slaughter methods and slower-growing breeds of broiler chicken (there’s a similar campaign in Europe called the European Chicken Commitment). Companies also seem to stick to the pledges they make in similar campaigns — for cage-free campaigns for egg-laying hens, around 90% of companies fulfil their cage-free pledges (although we’d guess more work needs to be done to make this happen in the future).

Here’s a breakdown of how the Better Chicken Commitment practices affect average chicken welfare:

Similarly, you might be able, using a small amount of resources, to get governments to act (and they have many, many more resources than even big companies). The EU is revising its animal welfare laws, and other European countries are also considering steps like banning caged hens. We think there are opportunities to help shape these reforms. In the US, it seems like ballot initiatives are almost as cost-effective as corporate campaigns. We’re particularly excited about the Good Food Institute’s work to leverage government funding for alternative proteins.

Third, we should look for interventions that the animal agriculture industry won’t fight — or, at the very least, which don’t require their support. This isn’t always doable, but if you can find ways to improve the lives of animals that won’t be fought, they’re likely to be particularly cost effective.

One great example here is developing laws in countries with relatively high-welfare farms that restrict the import of low-welfare products, as this benefits both animals around the world and domestic farmers.

Another example is working on technological progress.

Some technological progress, such as technologies to prevent the conception of male chicks or immunocastration for piglets, could substantially improve the lives of farmed animals — and many have only small costs for farmers (e.g. in-ovo-sexing, which ensures all chicks born are female, increases the costs of egg production by around 1–3 cents per egg).

We’d also like to see research on ways of reducing keel bone fractures, as these are a major cause of suffering in laying hens, and may be worse in cage-free systems. More speculatively, we might be able to gene-edit animals to prevent them from feeling pain.

If we can find suffering-reducing technologies that are cheap to use, it may be easy to get farmers to use them (as we’re seeing with in-ovo-sexing).

Fourth, importantly, we need to find solutions that don’t accidentally cause harm.

As an example, we might be able to convince people not to eat beef on environmental grounds or by raising the price of beef through welfare interventions. But this might lead to people eating chicken instead — and not only do chickens live in much worse conditions, but they’re smaller, so many more chickens are killed for the same amount of meat. The same problem arises even more so for switching to small fish and smaller invertebrates like shrimp.

Finding solutions that are very unlikely to cause harm is much harder than it sounds — there are plausible reasons why many of the solutions we’ve discussed above could cause harm. If you develop a technology that improves animal welfare (like immunocastration or in-ovo sexing), but this technology lowers costs for farmers, it also might decrease prices, increasing the demand for animal products and so increasing the number of animals in factory farms, resulting in more harm. Weighing up these effects is hard, and price-decreasing technologies may well end up being good overall — but because of the plausibility of harm, they’re unlikely to be among the best approaches to solving factory farming, so we’d avoid working on them if you have other options.

As another example, corporate campaigns to get farms to switch to slower-growing breeds of chicken improves the welfare of the chickens, but these slower-growing breeds live longer, which might lead to more suffering overall. Corporate campaigns might also support humanewashing — convincing people that meat is high welfare when it’s not, encouraging people to buy low-welfare products. Overall, we still think many corporate campaigns are worth doing — but it’s important to investigate possible sources of harm when choosing what to work on.

In some cases, people have stopped their work because of this kind of risk. Anima International were campaigning to end live sales of carp in Poland. They became worried about carp being replaced with salmon, a carnivorous fish, and as a result increasing the number of fish farmed overall — and so ended their campaign. We think this is extremely commendable!

Some writers on animal welfare, such as Brian Tomasik go further and suggest avoiding most welfare interventions and instead focusing on improving slaughter — as slaughter improvements don’t introduce other complicating factors like changing the length of time animals live.^[162]

We’re not saying you need to be certain that the intervention you work on doesn’t cause harm — that’s just not possible. But it’s important to do what you can to think through the downsides and try as much as you can to avoid interventions that sound good and which might even do some good, but which are bad ideas overall because they may cause more harm.

Finally, if you can work in a particularly neglected sub-area of the issue, your solutions are more likely to be cost-effective overall. This is because solutions usually have diminishing returns to effort.

As we’ve seen, the vast majority of the animals in factory farms are fish and invertebrates (like crustaceans and insects). Work on these animals (like getting any aquatic welfare standards or finding better ways of slaughtering shrimp) seems pressing. We also think work to prevent the rise of insect factory farms seems particularly pressing.

Similarly, work in non-western countries is likely to be more cost-effective overall.

Work on factory farming is highly neglected

We’ve argued so far that factory farming is large in scale, and that there are promising ways of solving the problem. But work in this area is also pressing because it’s so neglected that the impact of an additional person working on it or donating to efforts in the area will tend to be high.

Philanthropic spending on preventing factory farming is around $290 million a year^[163] — which is similar to philanthropic spending on other issues we prioritise (like risks from AI and nuclear war), and over 100 times less than areas like global development (around $70 billion) or climate change (around $60 billion). Open Philanthropy, the largest single funder of farmed animal welfare work,^[164] told us that they expect total spending in the area to grow to around $450 million a year over the next decade.

This spending corresponds to something like 1,750 to 2,000 people working on this problem full time, growing to something like 2,500 to 3,000 people over the next decade.^[165]

There’s also work being done in the private sector, especially in alternative proteins. There are something like 55,000 people total working for companies in the area (like Quorn, Gardein, and Beyond Meat). We’re uncertain how to count these people — most of what they’re doing is delivering products into supermarkets, which is helpful, but not really focused on advancing the field or ending factory farming. Only around 300 of these 55,000 roles are focused on cultivated or plant-based meat research.

If we focus only on work we think directly addresses the issue of factory farming (e.g. alternative protein research roles), spending from the private sector is more like $120 million per year, with around 750 people working on the problem.^[165]

That means altogether, we’d estimate ~3,000 people are working on reducing harms from factory farming and around $410 million is dedicated to this issue.

Within that, there are areas that we see as particularly neglected. Around 10 people are working full time on insect farming and maybe around 20–30 on shrimp farming.^[166] And it seems like Open Philanthropy’s donors have decided not to fund work on invertebrate welfare, so these areas are particularly neglected in funding. We’d also guess that factory farming in developing countries tends to be more neglected.

How can we compare the pressingness of factory farming to existential risks?

We think that reducing risks to the continued existence of civilisation is a particularly pressing moral issue.

This is reflected in our list of the world’s most pressing problems. Our top problems include:

All of these are prioritised so highly at least in part because we think they are existential risks.

So, in order to figure out how highly we should prioritise the problem of factory farming, we think it makes sense to try to compare it with existential risks.

This kind of comparison is going to be especially uncertain – this research is extremely challenging and there’s not much existing work to draw on. We’d like to see more researchers try to tackle these questions, but for the time being we will try to sketch our own comparison here.

We’ll start by trying to compare the scale of these problems: how much good would be achieved if we completely solved each of these problems?

To simplify things, let’s try to compare factory farming directly with just the problem of nuclear weapons as an illustration of the kind of analysis needed.

We think the risk of nuclear war presents a large-scale problem. There are two reasons for this:

A large nuclear war would have catastrophic immediate consequences, killing billions and causing unimaginable suffering — and it would reduce the size and probably quality of life of the population for many decades.
Then there’s a small but real chance (we’d guess something like 1 in 10,000) that such a war could lead to the complete collapse of civilisation, and even human extinction. This would have very long-run implications: there would be no more human civilisation, ever. Since the number of future individuals whose lives matter could be vast, the expected value of reducing risk to those lives could also be large.

Above, we looked at how many animals count morally the same as one human. We saw that from a welfarist perspective, there are two components to this:

Animals are worthy of moral consideration if they are conscious, so we need to consider the chances that each animal is conscious.
Animals have different welfare ranges (i.e. capacity for wellbeing). We looked into the most recent and most comprehensive research that’s been done on this topic — Rethink Priorities’ Moral Weight Project.

If we use the mean moral weights from the Moral Weights Project (that include both the welfare ranges and a weighting for the probability that each animal is conscious), and we multiply those weights by the number of animals of each species studied, we find that we kill the moral equivalent of 160 billion humans each year through factory farming, from a welfarist perspective.

There’s huge uncertainty on this figure. Just looking at uncertainty in the welfare ranges, this figure might vary from 60 million to around 800 billion (using the 5th and 95th percentile estimates respectively). And that is before taking into account uncertainty that this is the right way to approach the question.

Still, let’s compare that to the immediate consequences of a nuclear catastrophe (putting aside the long-run implications for now). A large-scale nuclear catastrophe could kill up to around 8 billion humans (the entire world population), and do so once — not every year.

Moreover, the suffering caused by the way we treat animals seems plausibly even worse than the suffering a nuclear war would cause its survivors.

This suggests the scale of factory farming is larger than (or perhaps similar to) the scale of the immediate consequences of a large nuclear war. Personally, I’d guess that, morally speaking, the scale of factory farming over the course of a few decades is something like 100 times larger than the scale of the immediate consequences of a large nuclear war.

It’s much harder to compare the scale of factory farming with the immediate consequences plus the potentially ultra long-term consequences of nuclear war arising from the existential risk that such a war might pose.

We argued above that some kind of value lock-in that perpetuates factory farming into the very long-run future seems highly unlikely, and that, over the very long run, we expect factory farming to end. That said, we might expect the effects of our actions on the welfare or number of farmed animals to persist for decades, and it could be centuries.

How you compare this with the long-run effects of nuclear war depends on how much you buy the arguments for thinking existential risks are top priorities due to their scale.

In short, those arguments say that:

We should care about how the lives of future individuals go. (If animals are worthy of moral consideration, or if we should care about digital minds, we need to consider them too).
The number of future individuals whose lives matter could be vast.
Those individuals’ lives are likely to be good overall — for example, with more flourishing than suffering (or whatever is relevant for a good life).
This means that it’s better for these individuals to be able to exist than for the universe to be empty. So there aren’t just a lot of lives in the future, there’s a lot of moral value in the future that we would lose if we went extinct or permanently reduced our potential as a species.
The expected scale of existential risk reduction, which can be calculated by multiplying the size of the risk by the value of the future, is therefore high. (This is just about the expected scale of reducing existential risks — in our article on existential risks, we also talk about the neglectedness and tractability of doing so. Many people view lower tractability as a reason not to prioritise existential risk reduction.)

We argue for the first two of these claims in our article on longtermism and think they are very likely to be true.

Whether future individuals’ lives are likely to be good seems much harder to answer — we’d guess the answer is yes, but that’s highly uncertain. In my view, this uncertainty substantially decreases the relative importance of existential risk reduction compared to other concerns.

The fourth claim (it’s good for individuals with good lives to exist) is controversial, but our guess is that it’s true. Read more about the arguments here.

The final claim — that the expected value of the future is high — relies on the idea that existential risk is going to be much lower in the future (otherwise, the expected number of future people ends up relatively small).

Finally, thinking in terms of expectations is a theoretical ideal, not a practical methodology. Making explicit estimates of expected scale (like by multiplying the size of a plausibly existential risk by the value of the future) is sometimes useful as a method, but we should also look for useful rules of thumb and robust arguments, or even use gut intuitions which can incorporate implicit understanding from experience rather than (just) explicit reasoning. And it’s not clear that all rules of thumb — even ones focused on improving the long-term future — suggest the scale of existential risk is larger than that of factory farming.^[167]

Given all this, I think a reasonable position to take is that we should think of nuclear war as a large-scale problem for both its short-run consequences and the existential risk it poses. If that’s right, then it’d be reasonable to think of these effects as comparable in scale — so that the existential risk’s contribution to the scale of the problem is between 10% and 90% of the total scale of the problem of nuclear war. Combining that with my view that the short-run effects of factory farming are plausibly 100 times more important than the short-run effects of nuclear war suggests that factory farming is overall larger in scale.

That said, while comparing factory farming to existential risks in general is extremely difficult, and it’s plausible factory farming is a larger-scale problem than nuclear war, we do think that factory farming seems smaller in scale than the existential risk posed by AI — as the existential risk from AI seems substantially larger than that posed by nuclear war.

As we’ve argued, factory farming is also highly neglected. It seems like it’s currently less neglected than preventing an AI-related catastrophe, but more neglected than most other issues we prioritise, like nuclear weapons or preventing catastrophic pandemics. We’d also guess that preventing an AI-related catastrophe is becoming less neglected faster than factory farming, so within a few years factory farming may be the most neglected of these areas.

We’re not really sure how to compare the solvability of factory farming to existential risks. Helping some animals — for example, through corporate campaigns — seems far more tractable than most ways of reducing existential risks, but it’s only addressing a small part of the overall problem. Large-scale changes to factory farming like ending big chunks of the industry seem much harder right now, maybe harder than substantially reducing existential risks, but as we’ve argued, we think it could become much easier as technology advances — and there are things we can do now to lay the groundwork. Overall, factory farming seems similarly solvable to other problems we prioritise (although we’re highly uncertain).

It’s worth underlining again that these comparisons are hugely difficult and under-researched, so no one should take this analysis as definitive. But, putting the above reasoning together into a best guess, I have come to think that factory farming is likely more pressing than smaller-scale existential risks like nuclear war, but less pressing than the plausibly much larger existential risk posed by AI. 80,000 Hours as an organisation continues to rank nuclear war as more pressing than factory farming, but there’s significant uncertainty and ongoing debates about these topics.

What are the major arguments against this problem being (especially) pressing?

We just gave one major argument: that factory farming probably doesn’t influence the long-run future, whereas existential risks do. If you find the arguments for focusing on issues that can affect the long-run future persuasive, that means that if an existential risk is substantial, it’s plausibly a larger-scale problem than factory farming.

Here are a few other reasons you could have for prioritising other issues above factory farming:

You might think that the wellbeing of each animal matters much less than the wellbeing of each human. If you think the difference is big enough, then you’ll think the scale of this problem isn’t as large (in terms of moral importance) as the scale of problems that affect current generations of humans, like global health or any imminent risks from pandemics, war, and AI.
You might agree with prioritising work on the long-run future, but think that there are other ways of affecting the long-run future other than working on existential risks — some people prioritise improving the trajectory of civilisation over preserving its existence. For example, you might think the way we treat digital sentience could have a bigger impact on the long-run future than the way we treat animals, if you expect there to be more digital minds than animal minds. If so, this suggests that you should work on digital sentience (or another issue that seems like it could affect the long-run future) instead.

There are also some reasons that you might be very pessimistic about our ability to make progress on ending factory farming — at least in a way that doesn’t worsen other issues:

You might worry that promoting concern for other beings increases risks of astronomical future suffering. This suggests you should work on s-risks instead.
You might think that work on farmed animal welfare could make lives worse for wild animals.
You might think that the lack of growth in veganism and pro-animal attitudes over the past decades (since an initial surge in popularity in the West) suggests that moral attitudes to animals are highly resistant to change. If you’re also sceptical about technological change ending factory farming, you might just think the problem is intractable.

What can you do to help?

When people think about working in animal welfare, they might picture looking after chickens in a sanctuary or handing out leaflets in a shopping mall.

But there are options that we think can achieve many times more impact than either of these options. A really high-impact job that’s working on reducing factory farming would focus on the ways of solving the problem that we discussed above.

As a result, the main options we recommend in this area are:

We’ll go into some detail about each of these below.

If you’re moving into the area for the first time, or early in your career, you could also try:

Joining a student fellowship or group (for example, the Alt Protein Project student groups, The Reducetarian Fellowship, the New Roots Leadership program, or the Southeast Asia Farm Animal Welfare Fellowship
Attending a conference that’s open to newcomers, but that’s attended by most of the main organisations in the space (for example, AVA or CARE). We’ve also been told that, if you can get a spot, EA Globals are some of the easiest places for people just starting out in the area to speak one-on-one with organisational leadership. (At purely animal-focused conferences, leadership figures are too popular!)

We’d also recommend taking a look at Animal Advocacy Careers as well as Hive, a Slack workspace and newsletter focused on farmed animal advocacy.

If you already have experience, it might be worth looking at what the main skill bottlenecks are to making progress on the problem in order to figure out where you can contribute best. When we spoke to people we know working on solving factory farming, they told us the main bottlenecks are:

Funding
Management and leadership
Government and policy expertise
Entrepreneurship and starting new organisations

We expect these to change over time, so they’re a less useful guide if you think you should currently be spending time building career capital and only aiming to have an impact later (which we often recommend for people who are early in their careers).

Of course, no matter what your job is, if you have more wealth than you need you can help by donating a portion of your income to the most cost-effective animal charities you can find. (See here for a few recommendations.)

Earning to give

As we mentioned, there’s very little funding for factory farming relative to many other causes.

So one of the best ways to help might be by earning to give, which means taking any job that’s higher paying in order to donate more.

Our top recommendations for earning to give — because they can pay so much — are:

These paths are highly competitive, but if you’re exceptionally successful, you could earn millions of dollars a year. If you donate most of that, that would mean increasing the funding for the whole cause area by something like 1% by yourself! If you take the time to make sure you’re donating to particularly effective opportunities, your impact could be even higher than that suggests.

We’d be particularly excited about people earning to give to support invertebrate welfare (e.g. insects, shrimp, and other crustaceans) because these areas aren’t currently being funded by large donors like Open Philanthropy.

Helping to run nonprofits

Many of the organisations working on the most cost-effective solutions are nonprofits.

These organisations need people to help run them. That might mean working in management, HR, finance, accounting, law, fundraising, software, operations, marketing, communications, and more.

According to Animal Advocacy Careers, nonprofits working on ending factory farming currently find it hardest to hire for leadership and fundraising positions. So if you’re a good fit for one of those, you might find your skills are especially useful.

The best way to get started if you don’t already have experience is probably by finding any role that will let you start learning relevant skills — even if that’s not initially at a high-impact organisation.

To learn more, including more information on how to get started, take a look at our article on organisation-building skills.

You could also look at:

Seren Kell

Seren did a degree in biochemistry and went straight into working in alternative proteins. But she didn’t go into research. Instead, she’s the head of the SciTech team at the Good Food Institute Europe. They are helping build the field of alternative proteins by identifying the barriers to growth and removing them — for example, by building funding and helping founders find collaborators. We’d guess this is even higher impact than directly working on alternative protein research because it’s so high leverage.

LEARN MORE→

Founding something new

Founding something is a difficult path — but, if you succeed, it can be hugely impactful.

There are two broad routes here outside founding a company for earning to give:

Founding a new nonprofit focusing on a gap in what’s needed to tackle factory farming
Founding a for-profit company that helps solve the problem — with the current best bet being alternative proteins (especially if you can find investment that wouldn’t otherwise be spent on alternative protein research)

Even if it doesn’t work out, you’ll probably learn a huge amount — so this can also be a great route for career capital.

If you’re starting a nonprofit, one option is to join an incubator, such as Charity Entrepreneurship or, if you’re in Southeast Asia, Welfare Matters’ Farmed Animal Welfare Incubator.

If you’re interested in founding an alternative protein startup, take a look at these resources from the Good Food Institute. The Good Food Institute also offers a mentorship programme for alternative protein entrepreneurs, a database of accelerators and incubators, and a community and events.

To learn more about this career path, read our career review on founding impactful organisations.

Andrés Jiménez Zorrilla

Andrés probably wouldn’t have guessed his career would end up focused on shrimp. While he was always interested in animal welfare, his early career was pretty normal — he studied economics at university and then went to work in real estate. In 2020, he pivoted his career through the Charity Entrepreneurship Incubation Program, and as a result he cofounded the Shrimp Welfare Project, which to date has helped over one billion shrimp.

LEARN MORE→

Government and policy

There are two broad areas for government and policy work on factory farming:

Improving welfare standards on farms — as we mentioned earlier, there are lots of exciting opportunities for legislative reform
Removing barriers to and leveraging government support for alternative proteins — most of this work is currently carried out by the Good Food Institute and its affiliates around the world

Working in policy might mean working in the executive branch, lobbying from the outside, or possibly even running for office.

Our article on policy and political skills goes into more detail, including a bunch of ideas about how to get started in the area.

Corporate campaigning and activism

Corporate campaigns — like those we mentioned above working on improving the lives of caged chickens — are one of the most cost-effective ways people have found of improving welfare for currently farmed animals.

So learning how to effectively carry out these campaigns is a particularly useful skill set, especially if you can then go on to run entire teams or organisations of campaigners.

We haven’t looked into this area much, but we’d guess the best way to get started would be to volunteer with an organisation doing corporate campaigns, like The Humane League.

Leah Garcés

Leah Garcés initially thought that the best way to help animals would be by becoming a vet. But while she was studying for a master’s degree at King’s College London, she discovered the world of professional activism. Her first job out of college, at the age of 22, was as an international campaign manager at Compassion in World Farming. She’s now the president of Mercy for Animals, an organisation focused on campaigning for the welfare of farmed animals.

LEARN MORE→

Scientific and engineering research

We think there are opportunities for scientists to help reduce factory farming by:

Developing alternative proteins
Working in animal welfare science

This work will probably require you to have a relevant degree. In both fields, biology or chemistry undergraduate degrees are useful; you can also do research into animal welfare with philosophy or neuroscience backgrounds.

About half of alternative protein job postings say they require a relevant postgraduate degree — either a relevant PhD or a master’s with multiple year’s additional industry experience. According to the Good Food Institute, relevant areas include: mycology, plant biology, molecular biology, cell biology, biochemistry, food science, genetic engineering, chemical engineering, mechanical engineering, bioengineering, tissue engineering, and materials engineering.

To get started on an alternative protein research career path, we’d recommend this newcomer’s guide from the Good Food Institute.

There are also lots of unanswered questions in animal welfare science. What are the relevant indicators for animal consciousness? How much pain do animals feel on farms in different situations? We have some vague answers to these questions, but better answers could importantly guide people’s actions — and we know far less for some animals, like fish and invertebrates.

For this article, we leaned heavily on the work of the Welfare Footprint Project, who carefully analyse the effects of things like the Better Chicken Commitment or banning gestation crates for sows. On insects, we’re excited about the work of the Arthropoda Foundation.

Most research in this area happens in academia (and even at organisations like the Welfare Footprint Project, most researchers have an academic background) — which again means you’ll likely need a relevant postgraduate degree. For more on academic careers, read our article on how to become an academic researcher.

There’s other potentially useful research, such as the development of in-ovo sexing and immunocastration. More speculatively, The Far Out Initiative is researching ways of genetically engineering animals who don’t suffer — I’d guess that at least some people should be engaging in this sort of research, but it’s much less likely to pan out than the other research we’ve mentioned in this section.

If you’re interested in a career in research and just getting started, we’d suggest reading our article on building research skills.

Strategy research and grantmaking

These roles involve figuring out what we should be doing to best help farmed animals, and then making that happen.

This might mean something like economics research in academia looking at the price elasticity of animal products to figure out where cost-increasing interventions should focus to have the biggest impact (or where cost-decreasing interventions could cause substantial harm), or becoming a grantmaker at a foundation looking to fund solutions to factory farming.

For academic research, you’ll want to pursue a PhD in economics, or get a degree in public policy or maybe philosophy. Doing similar research at a think tank or nonprofit might not require an advanced degree, but it’s probably still useful.

For becoming a grantmaker, you should probably start by doing any other work in animal welfare, building up your expertise and connections. (Read more about how to become a grantmaker.)

You could also try testing your fit for research and strategy roles by doing a research project in your spare time or funded by a grant, perhaps on a topic from Open Philanthropy’s list of social science research topics for animal welfare.

Lewis Bollard

After graduating with a law degree, Lewis started out his career as a consultant, before moving to work as a litigation fellow at The Humane Society of the United States. He now leads Open Philanthropy’s farm animal welfare grantmaking.

LEARN MORE→

Find vacancies on our job board

There are also other job boards that you might find helpful, including:

Animal Advocacy Careers’ job board covers jobs in a range of areas we think are particularly impactful.
Alt Protein.Jobs and Alt Protein Careers focus on alt protein jobs, while ForceBrands and Indie Bio cover a wider range of related jobs (which may be useful for career capital).
Vegan Job Board and VeganJobs focus on advocacy and nonprofits.

Key organisations

The main funders and grantmaking organisations (donating $500,000+ a year) are:

Open Philanthropy — the largest funder in the area
The Navigation Fund, which works primarily on influencing dominant institutions to care more about farm animal welfare
Focus Philanthropy, which focuses solely on reducing the harms of animal agriculture
The Craigslist Fund (yes, that craigslist), which also focuses on factory farming
Farmed Animal Funders, a decentralised funding collaborative which helps funders make decisions about animal welfare donations
EA Funds, a platform for moving money to particularly cost-effective and altruistically impactful projects, which has an animal welfare fund
Animal Charity Evaluators, which evaluates animal charities and compares their effectiveness, influencing around $10m a year
The Food Animal Concerns Trust, which directs grants to farmers and others to support humane farming methods

There are more animal grantmakers on this list.

Organisations working on alternatives to animal products:

The Good Food Institute works to support the industry in the US. They help with field-building through grants, infrastructure, research, and bringing in private sector funding. They also work in policy, leveraging funding for alternative proteins and removing policy barriers.
The Good Food Institute has affiliate organisations around the world: GFI Asia Pacific, GFI Brasil, GFI Europe, GFI Israel, and GFI India.
There are thousands of companies working on some kind of animal product alternatives. We’d suggest looking at Alt Protein.Jobs and Alt Protein Careers for jobs in the area.

Some particularly relevant governmental and intergovernmental organisations:

The European Commission, in particular the Directorate-General Sante (unit G3 is responsible for animal welfare and unit E2 is responsible for regulations around novel foods, including alternative proteins), the Directorate-General Agriculture (unit E3 is responsible for animal products) and the Directorate-General Research and Innovation (unit B2 is resposible for research and innovation in alternative proteins).
The US Department of Agriculture is responsible for most animal welfare policy in the US.
The UK Department for Environment Food and Rural Affairs is responsible for most animal welfare policy in the UK.
The UK Animal Sentience Committee examines UK government policy to see whether it fully considers the welfare needs of animals as sentient beings.
The World Organisation for Animal Health focuses on animal disease control and has 183 member states.

Lobbying and campaigning organisations, focusing on both the government and corporations. Here are some of the top organisations around the world:

The Humane League conducts corporate campaigns, with a particular focus on farmed chickens. They founded the Open Wing Alliance, a global anti-cage coalition.
Mercy for Animals work on undercover investigations of factory farms, government lobbying, and corporate campaigns.
The Albert Schweitzer Foundation lobbies the German government and corporations, as well as working on class action lawsuits and talking to consumers. They also have an organisation in Poland.
Animal Equality does investigations of farms, corporate outreach, and legal advocacy, as well as public education projects.
Eurogroup for Animals is a pan-European organisation focusing on EU legislation.
Wakker Dier runs campaigns for farm animal welfare in the Netherlands.
Fórum Animal works on animal welfare in Brazil.
Anima International focuses on investigating farms and corporate campaigns, working in several European countries.
Observatorio de Beinestar Animal works on corporate and government lobbying in Spain.
Sinergia Animal does corporate outreach, policy work, and investigations in South America and South East Asia.
The Accountability Board engages in shareholder activism.
Çiftlik Hayvanlarını Koruma Derneği conducts corporate, individual, and media outreach in Türkiye.
Legal Impact for Chickens does corporate outreach and litigation work in the US.
Compassion in World Farming conducts a wide variety of campaigns in the UK focused on ending factory farming.
Animals Aoteoroa campaigns on chicken welfare in New Zealand.
Voters for Animal Rights helps elect US political candidates who support animal welfare reform.

Organisations focused on dietary change:

Veganuary has played a significant role in promoting vegan food in the UK and now has campaigns across the EU, India, South Africa, and the US.
Dansk Vegetarisk Forening promotes plant-based products in Denmark.
China Vegan Society focuses on vegan movement-building in China.

Meta organisations, which help build the animal movement. Here are some of the top organisations around the world:

Hive runs an active slack community and public events for the animal advocacy movement.
Ambitious Impact runs programs like the Charity Entrepreneurship incubation programme, starting new charities focused on global health and animal welfare.
Faunalytics conducts useful research for animal advocates.
New Roots Institute educates students in the US about animal agriculture.
Catalyst is building an animal welfare movement specifically in Thailand.
Welfare Matters is building an animal advocacy movement across Southeast Asia.
Animal Alliance Asia is also focused on creating a cross-Asia animal welfare community.
Animal Advocacy Africa is trying to build an animal advocacy movement in Africa.
Rethink Priorities and Animal Ask do research that tries to resolve important strategic questions for animal advocacy.
Animal Advocacy Careers provides online advice, a job board, and other resources to help people have high-impact animal advocacy careers.
For a more comprehensive list covering organisations in a range of countries across the world, take a look at Animal Charity Evaluators’s List of Farmed Animal Advocacy Organisations.

Organisations focused on fish and crustacean welfare:

Fish Welfare Initiative works with farmers in India, China, and the Philippines to improve welfare standards.
fair-fish international association gathers information on fish welfare into the fair-fish database.
FishEthoGroup promotes research and gives consultancy and training on fish welfare.
Aquatic Life Institute helps promote animal welfare standards in fisheries and aquaculture through a certification campaign and policy work.
Crustacean Compassion campaigns for the legal protection and humane treatment of decapod crustaceans in the UK.
Shrimp Welfare Project aims to promote the adoption of electrical stunning technology in the shrimp industry, as well as working with farmers in India and Vietnam on welfare standards, and conducting research.

Other nonprofit organisations working in the area:

Insect farming and insect welfare charities, such as The Insect Institute and The Insect Welfare Research Society.
The Welfare Footprint Project is trying to quantify and map animal welfare across different living conditions.
Innovate Animal Ag works on finding technological solutions to animal welfare problems, like in-ovo sexing and on-farm hatching.
The Humane Slaughter Association helps farmers slaughter animals in higher-welfare ways.
Global Food Partners are a consultancy to help companies in Asia meet cage-free goals.

Learn more

Top recommendations

Animal Advocacy Careers provides articles, advice, and a job board to help you find a career to try to end factory farming
Podcast: Lewis Bollard on the 7 most promising ways to end factory farming, and whether AI is going to be good or bad for animals
Podcast: Seren Kell on the research gaps holding back alternative proteins from mass adoption

Further recommendations

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Data on the proportion of animals in factory farms is hard to find — not least because the definition of factory farm is fuzzy. In this article, we’ll try to explain how animals are usually treated in the vast majority of commercial farms.
We can get some data on this question from the United States Environmental Protection Agency, which talks about “concentrated animal feeding operations” (CAFOs), defined by the USDA as farms where animals are confined for 45 days or more in any 12-month period, and where the number of animals confined reaches a certain threshold, depending on the species, and where wastewater is managed in a certain way.
We’d guess that almost all CAFOs are factory farms, but that many non-CAFOs are also factory farms, either because they have animals in high-density conditions but have few animals, or because they have good wastewater management — so they don’t have the sort of environmental or pollution impact that the EPA cares about.
The Sentience Institute combined EPA data on CAFOs with USDA Census of Agriculture data on total animal populations (see the numbers in this spreadsheet to find the % of animals in factory farms in the US.
They found that 98% of land animals in the US were factory-farmed in 2017:
- 99.96% of broiler (meat) chickens
- 98% of egg-laying hens
- 99.9% of turkeys
- 98% of pigs
- 70% of cows
Unfortunately, there’s little data on the rest of the world. Based on our understanding of the regulatory landscape, we’d guess the situation is better in the EU but at least as bad elsewhere.
We’d also guess that the situation for fish is even worse than for broiler chickens. As far as we can tell there is both very little regulation about fish welfare and very little consumer demand for high-welfare fish.
We discuss more about how each animal is commonly treated below.
If the number of animals is roughly proportional to population, keeping in mind that 90% of animals in the EU are factory farmed (which we’d guess is an underestimate) and 98% of animals in the US and elsewhere are factory farmed, then approximately 97.5% of animals globally are factory farmed.
For more discussion, see How many animals are factory farmed by Hannah Ritchie at Our World in Data.
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Rethink Priorities researcher Saulius Šimčikas collated estimates of global captive vertebrate numbers. We used these estimates for this article.
We chose this research because it’s a collation of figures from the most widely used source — the Food and Agriculture Organization of the United Nations statistics database, FAOSTAT. Where FAOSTAT data was unavailable Šimčikas used reasonable sources and noted his uncertainty, giving ranges instead of point estimates. For example, for the number of farmed fish, Šimčikas based his estimate on data from Fishcount (who later published that data under peer review) and noted its high uncertainty.
Šimčikas noted issues with FAOSTAT and discussed at least one of these with the Food and Agriculture Organization who agreed there was a mistake.
Overall, this source seems comprehensive,fairly reliable, and unlikely to be biased in any particular direction (even though Šimčikas was an animal advocacy researcher when he wrote the post).
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Reliable estimates on the number of invertebrates in farms are harder to find than estimates for vertebrates. We relied on four sources:
- Insects raised for food and feed — global scale, practices, and policy by Abraham Rowe, which was based off production tonnage estimates completed by Barclays, the International Platform for Insects as Food and Feed (IPIFF), and other researchers, as well as conversations with farmers and the insect industry.
- Shrimp: the animals most commonly used and killed for food production by Daniela Waldhorn and Elisa Autric, which was based off production tonnage estimates from the Food and Agriculture Organization of the United Nations statistics database, FAOSTAT.
- Snails used for human consumption: The case of meat and slime by Daniela Waldhorn, also based off FAOSTAT.
- Data on non-shrimp crustaceans from Fishcount.
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In general, animal welfare rules and standards are stronger in European countries (in particular Austria and Sweden) than elsewhere in the world.
For more details see the Animal Protection Index which ranks countries by their animal protection policies, and Why did the EU lead the world on farm animal welfare and how can it lead again? by Lewis Bollard.
At the same time, compliance rates in the EU range from around 90% to around 20%, depending on the regulation (and the way in which compliance rates are estimated) — for a collation of work on this topic, see Do countries comply with EU animal welfare laws? by Neil Dullaghan, a researcher at Rethink Priorities.
Together, this suggests that European standards for conditions are likely substantially better than the actual conditions in which the vast majority of farmed animals — in European countries and elsewhere — are kept.
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We kill around 5 to 70 trillion wild marine animals every year (mainly shrimp), and between 100 trillion and 10 quadrillion smaller invertebrates, primarily through the use of pesticides. For completeness, we could also consider human effects on nematodes and zooplankton, which are likely extremely large in scale, but these tiny animals are generally poorly studied and everything about them (how many there are, how humans affect them, and whether they feel pain) is extremely uncertain.
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According to a scientific opinion from the European Food and Safety Administration:
The EU is one of the world’s biggest producers of poultry meat with around 6 billion broiler chickens being reared for meat every year resulting in 13.3 million tonnes of poultry meat. Overall, broiler farming in the EU is characterised by high intensification with the majority of birds reared indoor, at high stocking densities and where birds are bred for rapid muscular growth, and slaughtered within 28–42 days of age.
Søren Saxmose Nielsen, et al. “Welfare of Broilers on Farm.” EFSA Journal, vol. 21, no. 2, 1 Feb. 2023, https://doi.org/10.2903/j.efsa.2023.7788.
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A systematic review of poultry production diseases reported an average ascites incidence of 5% in flocks (see Table 2 of Jones et al., 2018), based on two studies of broiler chickens in a lab setting and one survey of ascites mortality rates in the UK in the 1990s.
Jones, P. J., et al. “A Review of the Financial Impact of Production Diseases in Poultry Production Systems.” Animal Production Science, vol. 59, no. 9, 2019, p. 1585, https://doi.org/10.1071/an18281.
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According to Granquit et al., 2019, which surveyed Norwegian farms
The aim of this study was to explore lameness and the associations between lameness and health/production measures of animal welfare in commercial broiler production, using the Welfare Quality® protocol for broilers. A total of 50 flocks were included in the sample and farm visits were conducted for lameness scoring at a mean age of 28.9 days… 19% of the birds showed moderate-to-severe lameness, which was associated with several production or health and welfare observations including feather cleanliness and condemnations as unfit for human consumption at slaughter.
For more on lameness in broiler chickens, see Schuck-Paim et al., 2022.
Granquist, E. G., et al. “Lameness and Its Relationship with Health and Production Measures in Broiler Chickens.” Animal, vol. 13, no. 10, 21 Mar. 2019, pp. 2365–2372, https://doi.org/10.1017/s1751731119000466.
Schuck-Paim, Cynthia, et al. “Quantifying the Welfare Impacts of Lameness in Broiler Chickens.” Quantifying Pain in Broiler Chickens: Impact of the Better Chicken Commitment and Adoption of Slower-Growing Breeds on Broiler Welfare, edited by Cynthia Schuck-Paim and Wladimir J. Alonso, Welfare Footprint Project, 1 May 2022. (Read the chapter as a google doc).
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For example, the minimum allowed stocking density for free-range chickens in the UK is 27.5kg/m².
If we assume broiler chickens weigh around 3kg (which is probably slightly heavier than the average broiler), then that’s 9.2 chickens per square metre, or 0.1 square metres of space.
The Better Chicken Commitment allows for a density up to 30kg/m² (6lbs / sq ft), resulting in slightly less space per cage-free chicken.
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Approximately 50% of heavy broilers (3.6 to 3.8 kg) reared on commercial farms in the Southeastern United States (US) present with some degree of [footpad dermatitis]. Furthermore, studies in Europe showed [footpad dermatitis] in 58% of the assessed commercial broilers. Besides on the feet, similar types of contact dermatitis can occur on hocks (hock burns) and the abdomen.
Freeman, Nathan, et al. “Remedying Contact Dermatitis in Broiler Chickens with Novel Flooring Treatments.” Animals, vol. 10, no. 10, 28 Sept. 2020, p. 1761, https://doi.org/10.3390/ani10101761.
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St-Pierre et al., 2003, estimated economic losses due to heat stress. As part of their analysis, they estimated the number of hours of heat stress pear year for poultry in various US states (see table 10) — this varied from around 100 hours per year (1% of the year) to around 1,000 hours per year (11% of the year), with an average of 668 hours / year (7.5% of the year).
For more on heat stress in broiler chickens, see Schuck-Paim et al., 2022. Schuck-Paim et al. note that the data in St-Pierre et al., 2003, is based on weather observations, which may not accurately capture the actual environment inside farms. They instead look at studies of bird behaviour — in particular, the frequency of panting to cool down — and conclude that:
An average proportion of 10 to 40% of birds within a typical flock of fast-growing broilers, growing near the maximum allowed density for the housing type used (close or open-sided), will be affected by heat stress in the last week of the 6-weeks growth cycle.
St-Pierre, N.R., et al. “Economic Losses from Heat Stress by US Livestock Industries.” Journal of Dairy Science, vol. 86, June 2003, pp. E52–E77, https://doi.org/10.3168/jds.s0022-0302(03)74040-5.
Schuck-Paim, Cynthia, et al. “The welfare impact of heat stress in modern breeds of broiler chickens.” Quantifying Pain in Broiler Chickens: Impact of the Better Chicken Commitment and Adoption of Slower-Growing Breeds on Broiler Welfare, edited by Cynthia Schuck-Paim and Wladimir J. Alonso, Welfare Footprint Project, 1 May 2022. (Read the chapter as a google doc).
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In order to determine the prevalence and risk factors for necrotic enteritis in broilers, a cross-sectional survey was conducted among 857 farms, rearing broilers for nine UK poultry companies… During 2001, 32.8% of the respondents indicated that they had
observed a case of necrotic enteritis (95% confidence interval, 29.1 to 36.8) in at least one flock. The disease was most often reported during the months October to February. The point prevalence (necrotic enteritis occurrence in the most recently reared flock) reported by farm managers was 12.3% (95% confidence interval, 9.8 to 15.2).
Hermans, P. G., and K. L. Morgan. “Prevalence and Associated Risk Factors of Necrotic Enteritis on Broiler Farms in the United Kingdom; a Cross-Sectional Survey.” Avian Pathology, vol. 36, no. 1, Feb. 2007, pp. 43–51, https://doi.org/10.1080/03079450601109991.
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A clinico-epidemiological study was therefore conducted at the District Veterinary Hospital, Kishoreganj, Bangladesh during October-November 2019 to determine the overall disease prevalence, prescription patterns, and disease associated factors in different bird types… Visceral gout (42.4%), coccidiosis (49.2%), and colibacillosis (24.2%) were the most frequent disease in broiler, Sonali, and layers, respectively.
Islam, Meherjan, et al. “Common Chicken Diseases in Kishoreganj, Bangladesh: Estimation through the Veterinary Hospital-Based Passive Surveillance System.” Advances in Animal and Veterinary Sciences, vol. 9, no. 11, 1 Jan. 2021, https://doi.org/10.17582/journal.aavs/2021/9.11.1951.1958.
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According to a scientific opinion from the European Food and Safety Administration:
The majority of broiler breeders will normally have restricted access to feed from about 7–10 days of age until the end of life. The severity of the feed restriction is high during the rearing period where the restriction level reduces the feed quantity down to 20–25% of what a broiler breeder pullet would eat if having ad libitum access to feed.
Nielsen, Søren Saxmose et al. “Welfare of Broilers on Farm.” EFSA Journal, vol. 21, no. 2, 1 Feb. 2023, https://doi.org/10.2903/j.efsa.2023.7788.
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According to an opinion from the UK Government Animal Welfare Committee:
At catching, carrying, collecting and loading, birds are exposed to welfare risks (for example injury, sudden large changes in temperature)… Due to the construction of feeder and watering systems in broiler and pullet barns, at thinning, feed and water are typically withdrawn from all birds, including those that will remain.
The opinion, which can be found here, goes into much more detail on the pre-slaughter process for poultry in the UK.
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Some hens are not stunned at all: 2.3% of total slaughtered meat chickens are not pre-stunned in the UK, according to 2022 data from Food Standards Agency (see the table on p.12).
Others are not effectively stunned, leaving them conscious for bleeding and slaughter. After assessing 10 Dutch farms and 10 Italian farms, de Jong et al., 2010, found that 7.1% of birds in the Dutch farms were not adequately stunned when exiting the stunner. However, this was true for only 0.01% of birds on the Italian farms.
de Jong, Ingrid, and Andrew Butterworth. “Part I Synthesis of the Farm Assessments in the UK, Italy and Netherlands.” The Assessment of Animal Welfare on Broiler Farms, edited by Bettina B. Bock and Ingrid de Jong, Welfare Quality Reports No. 18, May 2010.
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Poultry are excluded from the Humane Methods of Slaughter Act, and are instead covered by the Poultry Products Inspection Act. According to a notice by the US Food Safety and Inspection Service:
Although there is no specific federal humane handling and slaughter statute for poultry, under the PPIA, poultry products are more likely to be adulterated if, among other circumstances, they are produced from birds that have not been treated humanely, because such birds are more likely to be bruised or to die other than by slaughter.
Pre-slaughter stunning is rare in countries across Asia (Sinclair et al., 2019).
Sinclair, Michelle, et al. “Livestock Stakeholder Willingness to Embrace Preslaughter Stunning in Key Asian Countries.” Animals, vol. 9, no. 5, 8 May 2019, p. 224, https://doi.org/10.3390/ani9050224.
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This has been widely studied. For example, Gentle et al., 2023, found:
Shackling of commercial poultry involves the insertion of each leg into parallel metal slots and holding the bird inverted for a period of time before stunning and slaughter. Nociceptors signalling noxious stimulation of the skin have been identified in the beak and feathered skin but not in the scaly skin of the leg… The electrical activity was recorded from single C-fibres dissected from the parafibular nerve in anaesthetized animals… After comparing these threshold measurements and the stimulus response data with previous measurements of the force applied to the legs during shackling, it was concluded that shackling is likely to be a very painful procedure.
For more on shackling, see part III.1 of Negro-Calduch et al., 2022, which also provides much more detail on the welfare implications of broiler slaughter more broadly.
Gentle, M J, and V L Tilston. “Nociceptors in the Legs of Poultry: Implications for Potential Pain in Pre-Slaughter Shackling.” Animal Welfare, vol. 9, no. 3, Aug. 2000, pp. 227–236, https://doi.org/10.1017/s0962728600022715.
Negro-Calduch, Elsa, et al. “Quantitative assessment of the welfare impacts of methods for the commercial slaughter of broilers.” Quantifying Pain in Broiler Chickens: Impact of the Better Chicken Commitment and Adoption of Slower-Growing Breeds on Broiler Welfare, edited by Cynthia Schuck-Paim and Wladimir J. Alonso, Welfare Footprint Project, 1 May 2022. (Read the chapter as a google doc).
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After assessing 10 Dutch farms and 10 Italian farms, de Jong et al., 2010, found that 7.1% of birds in the Dutch farms were not adequately stunned when exiting the stunner. However, this was true for only 0.01% of birds on the Italian farms.
de Jong, Ingrid, and Andrew Butterworth. “Part I Synthesis of the Farm Assessments in the UK, Italy and Netherlands.” The Assessment of Animal Welfare on Broiler Farms, edited by Bettina B. Bock and Ingrid de Jong, Welfare Quality Reports No. 18, May 2010.
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The 2021 US United Egg Producers guidelines say:
Space allowance should be in the range of 67 to 86 square inches of usable space per bird to optimize hen welfare.
That’s 0.04m² to 0.05m².
In the EU, battery cages are banned, but the majority of laying hens are still housed in ‘enriched cages’ which are required to be at least 0.075m², according to Council Directive 1999/74/EC.
The welfare implications of this lack of space are set out in Schuck-Paim et al., 2021.
Schuck-Paim, Cynthia, and Wladimir J. Alonso. “The Burden of Psychological Pain in Laying Hens: Behavioral Deprivation.” Quantifying Pain in Laying Hens: A Blueprint for the Comparative Analysis of Welfare in Animals, edited by Cynthia Schuck-Paim and Wladimir J Alonso, Welfare Footprint Project, 2 Aug. 2021.
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Laying hens are highly susceptible to osteoporosis (Whitehead et al., 2000) which can lead to spontaneous bone fractures, especially of the keel bone. According to Toscano et al., 2020:
The [keel bone fracture] issue has also been cited as a major problem by the European Food Safety Authority Panel on Animal Health and Welfare (Welfare. 2015) and a North American–based consortium of welfare researchers (Lay et al., 2011)…
The number of affected birds within commercial flocks can range between 20 and 96%, based on reports from various countries including Belgium (Heerkens et al., 2015), Canada (Petrik et al., 2015), Denmark (Riber and Hinrichsen, 2016), The Netherlands (Rodenburg et al., 2008), Switzerland (Kappeli et al., 2011; Stratmann et al., 2015b,a), and the United Kingdom.
Whitehead, C.C., and R.H. Fleming. “Osteoporosis in Cage Layers.” Poultry Science, vol. 79, no. 7, July 2000, pp. 1033–1041, https://doi.org/10.1093/ps/79.7.1033.
Toscano, Michael J., et al. “Explanations for Keel Bone Fractures in Laying Hens: Are There Explanations in Addition to Elevated Egg Production?” Poultry Science, vol. 99, no. 9, 1 Sept. 2020, pp. 4183–4194, https://doi.org/10.1016/j.psj.2020.05.035.
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According to the 2022 Overview Report on the Protection of the Welfare of Laying Hens at All Stages of Production by the European Commission:
Forced moulting is implicitly banned in the EU through Directive 98/58/EC requirements, as it involves long periods of darkness and severe feed restriction.
In the US, there is no legislation, but the United Egg Producers guidelines say “only non-feed withdrawal molt methods will be permitted after January 1, 2006.”
Feed-withdrawal moulting is still standard practice in other regions (Lei et al., 2023):
At present, most laying-hen facilities in China use the fasting method, but with international emphasis on animal welfare, scholars have begun to find ways to improve production efficiency while ensuring animal welfare standards are adhered to.
Lei, Meng, et al. “Effects of Non-Fasting Molting on Performance, Oxidative Stress, Intestinal Morphology, and Liver Health of Laying Hens.” Frontiers in Veterinary Science, vol. 10, 28 Feb. 2023, https://doi.org/10.3389/fvets.2023.1100152.
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Schuck-Paim et al., 2021, survey the literature on the frequency of egg peritonitis:
[Egg peritonitis] has been shown to be the main cause of mortality in commercial layers by various studies… For example, in a flock of Babcock White Leghorns kept in single-tier aviaries in Canada, egg yolk peritonitis accounted for 22% of all deaths over a period of 33 weeks [70]. In another study conducted with 1,800,000 hens in conventional cages, and 118,000 hens in furnished cages, the proportion of deaths attributed to egg yolk peritonitis, salpingitis, internal layer and egg bound was respectively 26.6%, 4.7%, 1.4% and 0.7%, totalling 33% of mortality, by far the most prevalent cause of death [60]. Similarly, in the only study that compared the causes of normal layer mortality across housing systems using standardized diagnostic definitions, egg yolk peritonitis (defined by the authors as the congestion of visceral vessels with the presence of egg yolk within the coelomic cavity) was diagnosed as the cause of death in 25%, 19% and 12% of the daily mortalities in conventional cages, furnished cages and multi-tier aviaries, respectively, with salpingitis (oviduct greatly distended with a fetid yellow, easily crumbled exudate) responsible for an extra 2%, 1.6% and 3% of the deaths, and internal layer/egg bound for 0.5%, 0.3% and 1.2%, respectively [63]. Thus, EGPS (which includes both conditions) accounted for 27.6%, 21% and 16.5% of the mortality in conventional cages, furnished cages and multi-tier aviaries, respectively.
Studies on the prevalence of non-fatal cases of EGPS are even more scarce, with only one investigation published since 2000 [73]. The study, which involved the culling of a random sample of seemingly healthy hens from 15 Danish flocks at the end of the laying period reported that 4.13% of hens in furnished cages and 5.57% in single-tier aviaries had infections in the reproductive tract (salpingitis, peritonitis and oophoritis combined) or chronic lesions (e.g. scarification and/or serosal fibrosis on abdominal organs), the non-fatal chronic form of EGPS (Figure 5.2 in the Chapter 5 [5]).
For an analysis of the welfare implications of egg peritonitis, see Negro-Calduch et al., 2021.
Schuck-Paim, Cynthia, and Wladimir J. Alonso. “The Prevalence of Welfare Challenges Affecting Laying Hens in Different Housing Systems.” Quantifying Pain in Laying Hens: A Blueprint for the Comparative Analysis of Welfare in Animals, edited by Cynthia Schuck-Paim and Wladimir J Alonso, Welfare Footprint Project, 2 Aug. 2021
Negro-Calduch, et al. “Egg Peritonitis Syndrome: A Painful and Prevalent Disease in Commercial Layers.” Quantifying Pain in Laying Hens: A Blueprint for the Comparative Analysis of Welfare in Animals, edited by Cynthia Schuck-Paim and Wladimir J Alonso, Welfare Footprint Project, 2 Aug. 2021
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A report by the Council for Agricultural Science and Technology reported that about 30% of cage-free hens in the US had outdoor access in 2018 (Jacob et al., 2018):
According to the USDA–AMS June 4, 2018, cage-free shell egg report (USDA–AMS 2018), there were almost 54 million cage-free egg layers in the United States during the month of May 2018. This represents 14% of all the table egg layers in the country (USDA–NASS 2018). This would include both confined and free-range production systems. Of the cage-free hens, almost 16 million were certified organic, which would have access to the outdoors. This would represent only 0.3% of the total hen inventory for May.
In the EU, all free-range hens are required daily access to outdoor space, while ‘organic’ hens are only required outdoor access for one third of their life see section 6 of the 2022 Overview Report on the Protection of the Welfare of Laying Hens at All Stages of Production by the European Commission.
But access to outdoor space doesn’t mean the hens actually go outside — only that they have a route to do so. According to Larsen et al., 2017:
In this exploratory study, we tracked free-range laying hens on two commercial flocks with Radio Frequency Identification (RFID) technology with the aim to examine individual hen variation in range use… Most of the hens in both flocks (68.6% in Flock A, and 82.2% in Flock B) accessed the range every day during the study.
Pettersson et al., 2019, found that:
There are many studies that have reported figures for range use in free-range hens, although these figures are often lower than consumer expectation, rarely exceeding 40%. Less information is available on range use by individual hens, particularly in large commercial systems… Many factors affecting percentage range use have been identified, often through observational studies of commercial flocks, particularly the effects of climate, shelter and flock size. However, certain factors are somewhat underrepresented in the literature. The effect of pophole size and elevation is little studied, likely because of the difficulty in manipulating this factor. Similarly, little research has examined external stocking density or space requirements on the range.
Jacob, Jacqueline P. , et al. Impact of Free-Range Poultry Production Systems on Animal Health, Human Health, Productivity, Environment, Food Safety, and Animal Welfare Issues. CAST. Issue Paper 61, July 2018.
Larsen, Hannah, et al. “Individual Ranging Behaviour Patterns in Commercial Free-Range Layers as Observed through RFID Tracking.” Animals, vol. 7, no. 12, 9 Mar. 2017, p. 21, https://doi.org/10.3390/ani7030021.
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A systematic review of keel bone fracture rates across housing conditions (Rufener et al., 2020) found similar rates of prevalence across caged and cage-free housing systems (see table 1).
Rufener, Christina, and Maja M Makagon. “Keel Bone Fractures in Laying Hens: A Systematic Review of Prevalence across Age, Housing Systems, and Strains.” Journal of Animal Science, vol. 98, no. Supplement_1, Aug. 2020, pp. S36–S51, https://doi.org/10.1093/jas/skaa145.
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Shuck-Paim et al., 2021a, conduct an analysis of the literature looking at the prevalence of injurious pecking in various systems. They conclude:
Thus, to make a first attempt at estimating the burden of pain endured by laying hens as a result of skin wounds we provisorily consider the prevalence ranges reported in this section (5-15% in conventional cages, 1 to 10% in furnished cages and 5 to 30% in cage-free aviaries). For vent wounds, the only study found was conducted in 2006, hence to the reported prevalence we add uncertainty intervals (3-8%, 1-4% and 5-15% in conventional cages, furnished cages and aviaries, respectively)…
0-0.16%, 0.03-0.24% and 0.15-0.8% of all birds in conventional cages, furnished cages and cage-free aviaries [are] likely to die from a cannibalistic attack if cumulative mortality ranges from 3 to 8%. Of these deaths, 60-90% are estimated to result from fatal vent pecking events, and the remaining from fatal cannibalistic attacks.
An account of the welfare implications of injurious pecking can be found in Schuck-Paim et al., 2021b.
Schuck-Paim, Cynthia, and Wladimir J. Alonso. “The Prevalence of Welfare Challenges Affecting Laying Hens in Different Housing Systems.” Quantifying Pain in Laying Hens: A Blueprint for the Comparative Analysis of Welfare in Animals, edited by Cynthia Schuck-Paim and Wladimir J Alonso, Welfare Footprint Project, 2 Aug. 2021
Schuck-Paim, Cynthia, et al. “Welfare Implications of Injurious Pecking in Laying Hens.” Quantifying Pain in Laying Hens: A Blueprint for the Comparative Analysis of Welfare in Animals, edited by Cynthia Schuck-Paim and Wladimir J Alonso, Welfare Footprint Project, 2 Aug. 2021
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We couldn’t find good data on the prevalence of beak trimming. According to an article in Canadian Poultry Magazine, although some member states of the EU have banned beak trimming, 80% of hens in Europe are still beak-trimmed as of April 2019. Beak trimming is allowed and likely common in the majority of countries including the UK, most of Australia, the US, and China.
Beak trimming is restricted in some organic standards
The US Department of Agriculture Laying Hen Welfare Fact Sheet (2010) discusses the negative effects of beak trimming on welfare:
Following beak trimming, several anatomical, physiological, and biochemical changes occur in cut peripheral nerves and damaged tissues. There is a considerable body of morphological, neurophysiological, behavioral and production research demonstrating the emergence of several markers of acute and chronic pain (e.g., persistent lethargy and guarding behaviors, reduced feed intake, and development of neuromas) as a result of trimming. This is of more concern when the beak trimming is conducted in birds which are 5 weeks old or older using a hotblade beak trimmer.
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Egg-laying hens are depopulated at around 1.5 to 2 years of age, according to industry sources. That means, if there are around 7–10 billion egg-laying hens alive at any one time, we’re breeding around 3.5–7 billion hens a year. For every female egg-laying hen born, there’s on average one male chick born since half of all chicks born are male. As a result, we cull around 3.5–7 billion male chicks every year.
In the EU and US, the approved methods for male-chick culling are maceration and gassing. Maceration is meant to be an instantaneous death, but according to a report for the European Parliament:
A 2019 study by the European Food Safety Authority (EFSA) found, however, that maceration may fail to protect the welfare of such animals. More specifically, EFSA identified certain risks to the protection of welfare during the maceration of chicks: slow rotation of blades or rollers, overloading of machinery, and rollers set too wide. This can result in failure to kill the chicks, leaving them conscious, and in pain, distress and fear.
While in-ovo sexing technologies are now available, a 2023 report by Innovate Animal Ag found that only 15% of male chicks were identified in-ovo in the EU, and the technology has not gained any traction in the US.
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The issues at slaughter are similar to those for broiler hens. For details, see Schuck-Paim et al., 2021.
Schuck-Paim, Cynthia, et al. “The Last Day of a Hen’s Life: Depopulation and Transport.” Quantifying Pain in Laying Hens: A Blueprint for the Comparative Analysis of Welfare in Animals, edited by Cynthia Schuck-Paim and Wladimir J Alonso, Welfare Footprint Project, 2 Aug. 2021
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Finding reliable sources on the prevalence of different stocking densities globally is challenging. To be conservative, we will focus on what is known about EU housing conditions of pigs.
The European Food Safety Authority reports that (Nierlsen et al., 2022):
Indoor group systems for pregnant sows and gilts represent the main housing system in the EU since 2013 (Commission Regulation (EC) 889/2008).
The keeping of gilts and dry sows in housing which combines an indoor area and an outdoor concrete area is seen mainly in small-scale traditional farms or in farms certiﬁed for organic production in many European countries (Fr ¨uh et al., 2013). The proportion of sows in the EU which are kept in this system is consequently small… The group size and space allowance can vary widely, although if on a certiﬁed organic farm, the pen must provide a minimum space per pig of 2.5 m 2 indoors plus 1.9 m 2 outdoors (Commission Regulation (EC) 889/2008).
In most European countries [the outdoor paddock] system is used to a very limited extent, mainly on farms which are certiﬁed for organic production (Fr ¨uh et al., 2013) or other niche label schemes. However, there are notable exceptions where large commercial herds for conventional production house their breeding sows in outdoor paddocks, as is the case for 40% of sows in the UK and a smaller number of herds in France and other countries in regions with suitable climate and soil type (Edwards, 1994). The animals are typically enclosed by electriﬁed fences and provided with bedded wooden or metal shelters. The group size and space allowance within a paddock are highly variable, depending on farm size and soil type.
Based on this, we think it is reasonable to conclude that the vast majority of pigs are kept indoors without access to the outdoors.
The EU pig protection policy stipulates:
Standards concerning floor area are set according to the weight of the animal: between 0.15 m2 for pigs weighing less than 10 kg and 1.0 m2 per animal over 110 kg; 1.64 m2 per gilt; 2.25 m2 per sow; 6 m2 for a boar (10 m2 if the boar is used for natural services).
Nielsen, Søren Saxmose, et al. “Welfare of Pigs on Farm.” EFSA Journal, vol. 20, no. 8, Aug. 2022, https://doi.org/10.2903/j.efsa.2022.7421.
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A report from the EU Reference Centre for Animal Welfare Pigs — aiming to support welfare inspectors assessing heat stress in pigs — describes the current EU policies on temperature:
There are hardly climatic legal requirements for pigs in the EU-regulations. However, on a national level rules can be stricter, but often formulated as “open norms”. Directive 98/58/EC states that the accommodation should “not be harmful” to the pigs, which can only be checked by animal based indicators given in section 4.2. However, legal limits are not available in most countries, with difficult enforcement as a consequence.
COUNCIL DIRECTIVE 2008/120/EC 3 (EU, 2008) Annex I, Chapter I, Article 3: The accommodation for pigs must be constructed in such a way as to allow the animals to: have access to a lying area physically and thermally comfortable as well as adequately drained and clean which allows all the animals to lie at the same time. Directive 98/58/EC (EU, 1998) Annex: Buildings and accommodation Article 10: Air circulation, dust levels, temperature, relative air humidity and gas concentrations must be kept within limits which are not harmful to the animals.”
The European Food Safety Authority report on the welfare of pigs on farms (Nielsen et al., 2022) identified heat stress as a pertinent welfare concern, particularly in modern agriculture and for sows in farrowing crates:
Selection for fast growth rates and larger more prolific sows makes modern pigs more sensitive to heat stress… ‘Heat stress’ was classified as highly relevant in sows housed in farrowing crates.
Temperatures above 25 degrees celsius were identified as the upper limit of the acceptable range for heat in farrowing and lactating sows:
Quiniou and Noblet (1999) investigated the influence of high ambient temperature on performance of lactating sows. Comparing five ambient temperatures (18, 22, 25, 27 and 29°C) maintained constant over the 21-day lactation period, they found that skin temperature increased with increased ambient temperature (34.6–37.4°C between 18°C and 29°C), whereas udder temperature reached a plateau at 25°C (38.3°C). Moreover, the respiratory rate increased from 26 to 124 breaths/min between 18°C and 29°C, indicating that the evaporative critical temperature, corresponding to the upper limit of the comfort zone was below 22°C. They thus concluded that temperatures above 25°C seem to be upper critical temperature for lactating sows.
Ambient summer temperatures are likely to exceed this range often, leading to even higher temperatures in indoor housing. A review of the effects of heat stress on meat quality indicates that heat stress is a common and substantial cause of reduced pork production (Gonzalez-Rivas et al., 2019):
More recently, and despite heat stress abatement strategies, the annual economic losses to the US swine industry during the summer months were estimated to be $900 million (Pollmann, 2010). Unfortunately, the harmful consequences of heat stress to animal health and production are likely to continue in the future, particularly if selection for improved production traits is prioritised against thermotolerance and climate adaptation.
Potentially due to the lack of specific regulatory requirements, it is difficult to find exact estimates of the proportion of pigs that are experiencing heat stress. One industry publication, Agrifuture Magazine (an outlet from the German Agricultural Society), presents data suggesting that the sows in farrowing crates from sampled farms experienced ambient temperatures about 25 degrees celsius ranging from 34–91% of the time during summer months in 2017.

Nielsen, Søren Saxmose, et al. “Welfare of Pigs on Farm.” EFSA Journal, vol. 20, no. 8, Aug. 2022, https://doi.org/10.2903/j.efsa.2022.7421.
Gonzalez-Rivas, Paula A., et al. “Effects of Heat Stress on Animal Physiology, Metabolism, and Meat Quality: A Review.” Meat Science, vol. 162, Apr. 2020, p. 108025, https://doi.org/10.1016/j.meatsci.2019.108025.
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The EU policy for the protection of pigs (Directive 2008/120/EC — minimum standards for the protection of pigs) allows for tooth clipping without any form of analgesia (see section ‘Painful operations on animals’). As a result, we think it’s likely that this is common globally.
The European Food Safety Authority report on the welfare of pigs on farms (Nielsen et al., 2022) identified tooth clipping as a welfare concern in Europe, highlighting both the painful experience, lack of analgesics, and poor acute and long-term outcomes for the majority of piglets:
Epidemiological data are scarce. However, there is considerable anecdoctal evidence indicating that tooth reduction is a frequent practice on EU farms (Chou et al., 2020a). It appears that shortening of suckling piglets’ teeth within the first day(s) of life is carried out in many countries worldwide (e.g. Fredriksen et al., 2009), and there is little reason to believe that this has recently changed (Prunier et al., 2020a).
…Tooth reduction is commonly carried out in the first days of life (Prunier et al., 2021). The procedure involves the shortening of the upper and lower third incisor and the canines (total of 8 teeth) to remove the sharp part of the teeth without opening of the dental pulp. However, as teeth can have different length this can easily go wrong. A maximum removal of the top third of each tooth is generally recommended, but in practice this varies considerably, from a small fraction to the whole tooth above the gum line being removed (Gallois et al., 2005; Fu et al., 2019).>
Traditionally, either manual clipping (performed using side‐cutting pliers, called ‘clippers’) or electronic grinders (tooth abrasion with a stone) are used. Data of the actual distribution of both practices are missing.
…The practices of grinding and clipping cause also acute pain and long‐term pain. Acute pain is associated with the short‐term effect of the procedure of teeth reduction, while long‐term pain is caused by subsequent inflammatory processes of the tissues involved.
The report concludes that:
1. Tooth reduction is a stressful procedure that if performed incorrectly causes short‐ and long‐term pain. In particular, clipping is inherently injurious.
2. Grinding to only blunt the sharp tip of the tooth does not injure sensitive tissue when correctly performed.
3. Risk mitigation measures to reduce the necessity for teeth reduction include sow management measures to promote optimal milk supply, and balancing the number of piglets with the number of teats.
4. In individual litter situations where tooth reduction can be justified, the most effective measure to prevent and mitigate welfare consequences is training of staff in correct procedures.
5. Although current legislation highlights teat damage as evidence to justify tooth reduction, facial damage to litter mates is a more related animal‐based measure.
Nielsen, Søren Saxmose, et al. “Welfare of Pigs on Farm.” EFSA Journal, vol. 20, no. 8, Aug. 2022, https://doi.org/10.2903/j.efsa.2022.7421.
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The EU animal welfare policy on the protection of pigs allows for tail-docking prior to the seventh day of life without any form of analgesia (see section “Painful operations on animals”). As a result, we think it’s likely that this is common globally.
The European Food and Authority report on the welfare of pigs on farms (Nielsen et al., 2022) identifies tail docking as a leading welfare concern in farmed pigs in Europe, summarising the evidence:
Tail docking is widely performed to reduce tail biting lesions in pigs raised under intensive conditions (De Briyne et al., 2018). However, while many evidence suggested that tail docking reduces the risk of tail biting lesions, other studies indicate this will not eliminate tail lesion totally (D’Eath et al., 2016; Lahrmann et al., 2017; Thodberg et al., 2018, reviewed by Prunier et al., 2020b). Tail docking causes acute and medium‐term pain in the pigs (see Section 6.3.2). Routine tail docking is therefore a systematic source of pain that affects all the reared pigs (Valros and Heinonen, 2015).
They conclude:
1. Welfare consequences of tail‐docking in piglets will include soft tissue lesions and integument damage, bone lesion and handling stress, causing the overarching welfare consequences of pain and fear.
2. Whilst tail docking is effective in reducing the risk of tail lesions, it is not necessary if husbandry practices and management are appropriate.
3. Tail docking is painful, with short and medium‐term negative welfare consequences including soft tissue lesions and integument damage, bone lesions (including fractures of the spinal vertebrae), handling stress, fear and pain.
Nielsen, Søren Saxmose, et al. “Welfare of Pigs on Farm.” EFSA Journal, vol. 20, no. 8, Aug. 2022, https://doi.org/10.2903/j.efsa.2022.7421
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1. The EU animal welfare policy on the protection of pigs allows for the castration of pigs prior to the seventh day of life without any form of analgesia.
  The European Food and Authority report on the welfare of pigs on farms (Nielsen et al., 2022) identifies castration as a leading welfare concern in farmed pigs in Europe, summarising the practice and prevalence:
  Castration is a traditional practice in many countries and is still practiced in the majority of EU pig farms. It aims at reducing aggressive and sexual behaviour in adult male pigs and avoiding boar taint (an offensive odour resulting from androstenone, skatole and indol compounds) in pork and pork products. On farm, the procedure usually involves rapidly cutting the skin (using a scalpel) and the spermatic cords (using a scalpel or an instrument called ’emasculator’ which cuts and squeezes the spermatic cord) without administration of anaesthesia nor analgesia in piglets under 7 days (here considered the ‘surgical castration’ method). Castration by tearing the spermatic chords, even if not allowed in Europe, is still being performed in some cases (Schmid et al., 2021).
  A recent scientific review on invasive procedures in piglets summarised the negative implications of this practice to piglet welfare, confirming that there is now neural (observed via brain electric activity), hormonal, metabolic and behavioural evidence of pain that can last well after the procedure (Prunier et al., 2021)…neural pain pathways in pigs and humans are very similar and that a strong homology between porcine and human nociceptive neuron exist (Prunier et al., 2021), suggesting that castration can result in severe pain to piglets. These results align with previous studies reporting pain in piglets during (Taylor and Weary, 2000; Taylor et al., 2001; Kluivers‐Poodt et al., 2012; Viscardi and Turner, 2018) and after the castration procedure (Prunier et al., 2006; Kluivers‐Poodt et al., 2007).
  It was estimated that only 5% of piglets received analgesia and anaesthesia and ~ 40% received analgesia (alone) in 18 countries during castration.
  Nielsen, Søren Saxmose, et al. “Welfare of Pigs on Farm.” EFSA Journal, vol. 20, no. 8, Aug. 2022, https://doi.org/10.2903/j.efsa.2022.7421.
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The EU animal welfare policy on the protection of pigs allows for the nose-ringing of pigs kept in outdoor husbandry systems, but some member states have banned the practice (e.g. the Netherlands, Austria, Sweden and Denmark). The EU tends to have higher animal welfare standards than other countries.
The EU Reference Centre for Animal Welfare Pigs, in response to a question about the effect of rooting on welfare, reported:
Pigs are highly motivated for rooting and other explorative behaviours to investigate their environment, to forage or to prepare a place to lie (Studnitz et al, 2007). In natural environments, sows spend about 30% of their waking hours rooting and about the same amount grazing (Stolba and Wood-Gush, 1989). Rydhmer and Canario (2013) confirm this and state that “on pasture, feed-related behaviors like rooting, grazing, and exploring substrate account for 75% of daily activity”. When sows are kept outdoors, the rooting behaviour may lead to removal of large parts of the grass cover, potentially resulting in minerals leaching to the ground water and leaving less plants for grazing. Nose ringing reduces or eliminates this behaviour, as rooting probably becomes painful.
…The rooting disc is very sensitive and innervated by a high density of sensory nerves. Although not quantifiable in any way, the application of rings by perforating the tissue, the healing of the wound and the use of the nose after ringing are likely to be painful. The use of anaesthesia during application is not common. Some cases of inflammation are reported. The aim of the ring is to make the use of the nose for deep rooting painful, or at least very uncomfortable. Studnitz et al. (2007) report that the total amount of exploratory behaviour (rooting, manipulating, sniffing and chewing) was not significantly affected by ringing, but rings prevented sows from rooting and increased chewing and manipulation behaviour in comparison to not ringed sows. They did not see signs of rebound in rooting motivation after ring removal.
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In response to a resolution from the American Veterinary Medical Association, Trace et a., 2005, conducted a review into housing for pregnant shows.
They found that gestation crates have severe welfare implications – although noted a few ways in which they are better than commonly-used group housing:
Most research to date indicates that generally accepted physiologic measures of stress are
similar for sows housed in individual gestation stalls and in group pens. On the basis of information available at this time, Task Force members considered it reasonable to conclude that stall housing is not more physiologically stressful to sows than group housing.
…Gestation stalls, particularly when used in conjunction with feed restriction, may adversely affect welfare by restricting behavior, including foraging, movement, and postural changes. Stereotypies related to behavioral restriction can be reduced by providing bedding, foraging material, roughage, or a combination of these. Simply providing space to turn around is unlikely to resolve these repetitive, non–purpose-directed behavior patterns.
…Other factors contributing to poor welfare in stalls and small, unbedded pens include lack of exercise, lack of environmental complexity, lack of rooting/chewing materials, and an inability for the sow to exert control over her environment.
…Aggression has been reported in all types of housing systems, but it is most often worse and sometimes severe in group housing. Vulva biting, one of the most common and serious aggressive interactions, most often occurs in group pens that do not allow for simultaneous feeding of sows (eg, those using electronic sow feeders).
…Injury rate is lower for sows housed in gestation stalls, compared with sows housed in groups.
The use of gestation crates varies around the world. There are bans in some US states (the US produces around 11% of the world’s pork). According to a 2022 report from the USDA:
Over the past two decades, multiple States have passed animal welfare regulations in hog production. These regulations ban the common practice of using gestation crates—metal enclosures used to house pregnant sows—or stipulate space requirements for animals to stand and turn around. In addition to restrictions during production, two of these States, California and Massachusetts, passed retail sales restrictions that prohibit the sale of pork originating from animals kept in gestation-crate systems or their direct offspring. Hog welfare regulations are concentrated in States with relatively small pork industries. The proportion of the national herd covered by gestation crate bans is currently estimated at 3 percent based on expected production in 2022. Except for Michigan, each State with existing bans on gestation crates has produced, on average, less than 1 percent of total U.S. pork production (in pounds) since 2018. Ohio will become the largest hog-producing State to ban gestation crates when its regulations go into effect in 2026. Based on State hog inventories in December 2020, projected coverage of the total U.S. hog herd and the breeding herd is expected to remain below 10 percent of hogs and pigs under current State regulations through 2026.”
The US situation may be a bit better than this picture paints though due to corporate policy initiatives and California prop 12 (implemented in 2024) which prohibits the use of gestation crates for more than 24 hours in a 30 day period and no more than 6 hours in a 24 hour period for all pork products sold in the state regardless of the origin of the product.
In the EU (which produces 18% of the world’s pork), the use of gestation crates is restricted but not banned:
Individual housing in stalls Under EU legislation, gilts and sows can be kept in this system only for a limited period of time, i.e. gilts from service up to maximum 4 weeks after service, and sows from weaning up to maximum 4 weeks after service.
Individual or gestation stalls are the main housing system for pregnant sows and gilts from service up to farrowing worldwide (Ryan et al., 2015). In the EU, they are not permitted for use beyond 28 days post-service (Commission Regulation (EC) 889/200820 ). Some MSs have stricter legislative restrictions on their use. For example, in the Netherlands, gilts and dry sows can only be held in stalls for a maximum of 4 days post-service, in Austria for a maximum of 10 days and Sweden not at all except for the actual insemination. In Denmark, in 2020 legislation has been passed that sows housed in buildings built after2015 must be loose housed from weaning to farrowing; from 2035 this requirement applies to all sows.Similarly, Germany passed a legislation in 2020 introducing a ban on sow stalls, but it will not become mandatory until 2030.
Here, ‘service’ refers to mating.
The Welfare of Farmed Animals (England) Regulations 2000 , The Welfare of Farmed Animals (Scotland) Regulations 2000, The Welfare of Farmed Animals Regulations (Northern Ireland) 2000 and The [The Welfare of Farmed Animals (Wales) Regulations 2001] collectively ban gestation crates cross the entire UK:
A pig shall be free to turn round without difficulty at all times. The accommodation used for pigs shall be constructed in such a way as to allow each pig to stand up, lie down and rest without difficulty; have a clean place in which it can rest; and see other pigs, unless the pig is isolated for veterinary reasons. The dimension of any stall or pen [NI: used for holding individual pigs in accordance with these Regulations] shall be such that the internal area is not less than the square of the length of the pig, and no internal side is less than 75% of the length of the pig, the length of the pig in each case being measured from the tip of its snout to the base of its tail while it is standing with its back straight.
It’s worth remembering that, as we noted earlier, compliance rates in the EU range from around 90% to around 20%, depending on the regulation (and way in which compliance rates are estimated). We’d guess there are similar rates of noncompliance elsewhere, e.g. in the US and UK.
In China (responsible for 50% of the world’s pork production), there are no specific policies defining the housing requirements for the welfare of pigs.
A 2008 study of farming practices suggests the the use of gestation crates is likely widespread in China (Li, 2008):
Gestation and farrowing crates are the most popular farming tool of Western invention. We noticed them in all 9 breeding farms. Two of these farms were in inland Jiangxi and Anhui. Their wide use across the country is therefore no exaggeration. Sow crates are popular because they ensure success of pregnancy and prevent breeding sows from crashing the piglets. Productivity and efficiency are the attractions. No farm workers and owners appeared to know that use of farrowing crates is to be phased out in European Union nations. According to the manager of a Liaoning breeding farm, his sows were generally confined up to 150 days in standard crates. All the interviewees of the breeding farms referred to such modern farming practice glowingly.”
However, more recently, specific Chinese pork producers (e.g. Quinglian Food Company, Da Bei Nong, and more) have made pledges to move away from gestation crates voluntarily to improve welfare standards. That said, we’re unsure how many sows are covered by voluntary pledges, and there’s no enforcement, so we’d guess the vast majority of sows in China are still kept in gestation crates.
Li, Peter J. “Exponential Growth, Animal Welfare, Environmental and Food Safety Impact: The Case of China’s Livestock Production.” Journal of Agricultural and Environmental Ethics, vol. 22, no. 3, 30 Dec. 2008, pp. 217–240, https://doi.org/10.1007/s10806-008-9140-7.
Rhodes, R. Tracy, et al. “A Comprehensive Review of Housing for Pregnant Sows.” Journal of the American Veterinary Medical Association, vol. 227, no. 10, Nov. 2005, pp. 1580–90, https://doi.org/10.2460/javma.2005.227.1580.
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The EU animal welfare policy on the protection of pigs allows farrowing crates.
The European Food Safety Authority identified individual farrowing crates as a main welfare concern of lactating sows (Nielsen et al., 2022). They summarise the overall situation:
Individual crates are the main housing system for farrowing and lactating sows. The sows are normally moved to the farrowing crates in the week before expected time of farrowing and removed after the weaning of the piglets. A farrowing crate consists of metal bars running along the length of the sow. Sometimes, additional metal bars are placed on the top of the cage to prevent the sow from jumping or climbing in the attempt to escape. The length of the crate is about 2 m with a width between 0.45 and 0.65 m. To allow assisted farrowing, an unobstructed area behind the sow or gilt must be present. The space provided in the crates allows the sow to stand up and lie down, but not turn around or walk.Nowadays, sows are substantially larger than 40 years ago (Moustsen et al., 2011; Nielsen et al., 2018) and they rear a larger litter for a longer lactation length than before. Therefore, physical and behavioural restriction have increased over this period, especially in crates which cannot be adapted to the length and width of the sows.
Farrowing crates were introduced with the aim to prevent crushing piglets by the sow and thus reduce piglet mortality (Edwards, 2002). However, aggressive behaviour towards the piglets has been shown to increase when the sows are crated as compared to sows in loose housing system (Jarvis et al., 2006). Sows in crated system showed also higher restlessness, which further increases the risk of overlying when the piglets try to access the udder (Ocepek and Andersen, 2017).
Nielsen, Søren Saxmose, et al. “Welfare of Pigs on Farm.” EFSA Journal, vol. 20, no. 8, Aug. 2022, https://doi.org/10.2903/j.efsa.2022.7421.
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The European Food Safety Authority report into pig welfare on farms (Nielsen et al., 2022) identified early weaning age as a welfare concern of piglets. In summary:
Under (semi‐) natural conditions, weaning is a gradual process involving changes in the pattern of nursing which begin from the first week of life and are completed by 13–17 weeks of age (see Section 3.2.5.1). In current farm conditions, piglets are typically weaned abruptly by removal from the sow at a much younger age than 13–17 weeks. A number of different welfare consequences result from this weaning practice because of the psychological stressors involved and the immaturity of the behavioural, digestive and immune system of the piglet at this time (Edwards et al., 2020).
1. Abrupt weaning results in a range of welfare consequences including separation stress, prolonged hunger, prolonged thirst, gastro‐intestinal disorders, and inability to perform sucking behaviour, which has further detrimental consequences for resting problems, group stress and soft tissue lesions and integument damage.
2. Weaning age has not been associated directly with tail biting, although there may be indirect effects via other welfare consequences (e.g. health‐related) of a poor weaning transition.
3. These welfare consequences increase exponentially with reducing weaning age and are particularly pronounced at weaning ages of less than 21 days and with artificial rearing systems. However, there is great variability between different studies and housing systems.
4. The welfare benefits of increasing weaning age over the range between 21 and 28 days do appear to be meaningful as a result of the increasing maturity of behavioural, digestive and immunological systems over this period.
5. There are inadequate data to assess the welfare consequences of weaning ages greater than 28 days but indications from the ABMs that have been investigated are that, under good management, any welfare benefits are less pronounced.
The report also describes standard practice for inseminating sows after the weaning:
Sows are typically served at their first standing heat post‐weaning. Service is either natural (by the boar) or by artificial insemination (AI).
Nielsen, Søren Saxmose, et al. “Welfare of Pigs on Farm.” EFSA Journal, vol. 20, no. 8, Aug. 2022, https://doi.org/10.2903/j.efsa.2022.7421.
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In the EU, pigs must be stunned prior to slaughter in accordance with mandatory stunning as set out by Article 4.4 of the Council Regulation 1099/2009, with the exception of animals subject to particular methods of slaughter prescribed by religious rites.
The European Food Safety Authority report on welfare of pigs at slaughter (Nielsen et al., 2020) indicates that electrical (i.e. electronarcosis) and controlled atmosphere (carbon dioxide) stunning are the most common at large slaughterhouses:
The stunning methods that have been identified as relevant for pigs can be grouped in three categories: (1) electrical, (2) controlled atmospheres and (3) mechanical.
Electrical methods include head-only and head-to-body. Controlled atmosphere stunning methods (CAS) include carbon dioxide (CO₂) at high concentration (defined in this opinion as higher than 80% by volume), inert gases and CO₂ associated with inert gases. The mechanical methods that have been described in this report are captive bolt, percussive blow to the head and firearm with free projectile. These methods are mainly used as backup method or for small-scale slaughtering as in small abattoirs or on-farm slaughter.
During phase 2 [stunning], pigs might experience pain and fear during restraint (in electrical and mechanical methods) and during exposure to CAS before loss of consciousness.
Furthermore, ineffective stunning will lead to persistence of consciousness during hoisting, sticking [throat cut] and bleeding. Recovery of consciousness might occur in effectively stunned animals if sticking was delayed or was not properly done. Both these situations will also cause pain and fear to animals and are considered an important animal welfare concern in the stunning process.
The stunning phase itself causes pain and distress. For example, multiple studies indicate that pigs find carbon dioxide exposure distressing and painful — the European Food Safety Authority report on pig welfare at slaughter concluded:
It has been demonstrated that pigs find CO₂ in high concentrations aversive and, given a free choice, they avoid such atmospheres (Raj and Gregory, 1995; EFSA, 2004). CO₂ itself causes irritation of the nasal mucosa and exposure is therefore inducing a painful sensation (Steiner et al., 2019). CO₂ has the potential to cause welfare consequences via three different mechanisms: (1) pain due to formation of carbonic acid on respiratory and ocular membranes, (2) production of so-called air hunger and a feeling of breathlessness and (3) direct stimulation of ion channels within the amygdala associated with the fear response (Raj, 2006; Beausoleil and Mellor, 2015; AVMA, 2020).
For head-only electrical stunning, the EFSA report concludes pigs experience pain and fear during the restraining phase, and if consciousness is regained:
During the restraining, the welfare consequences are pain and fear. After stunning, if the stunning is ineffective or if the animals recover consciousness, the welfare consequences are pain and fear due to persistence of consciousness. Therefore, consciousness is not a welfare consequence per se but a prerequisite for experiencing pain and fear.
After stunning, pigs are ‘stuck’ (i.e. their throats are cut) and exsanguinated (i.e. bled out until death). Some pigs will be conscious during this phase even when pre-stunned.
A field study of slaughterhouses in Switzerland, Austria, and Germany found high rates of insufficient stunning prior to throat cutting leading to pigs being conscious during the throat cut and bleeding phase of slaughter (von Wenzlawowicz et al., 2022):
The proportions of assessments in which there were no failures were 28% (captive bolt), 12% (electrical stunning; pen), 21% (electrical stunning; trap), 31% (electrical stunning; automatic restrainer) and 13% (controlled atmosphere CO₂). The mean percentages of animals showing signs not compatible with sufficient depth of stunning were 13.5 (± 19.0)% (captive bolt), 12.5 (± 16.4)% (electrical stunning; pen), 10.9 (± 11.4)% (electrical stunning; trap), 3.2 (± 3.3)% (electrical stunning; automatic restrainer) and 7.5 (± 13.0)% (controlled atmosphere CO₂) showing a high variability between premises assessed.
During the sticking process, some pigs will receive multiple throat cuts due to failure of the first cut, increasing the time between the stunning and death and putting them at higher risk of regaining consciousness (Nielsen et al., 2020):
It is also important to note that effective captive bolt stunning of pigs leads to severe convulsions which may impede prompt and accurate sticking, especially if the pig is not restrained appropriately… Various studies have shown that up to 13% of pigs required more than a single sticking attempt to bleed out properly (Anil et al., 2000; Spencer and Veary, 2010).This hazard can lead to recovery of consciousness. There are no published data concerning this hazard.”
Nielsen, Søren Saxmose, et al. “Welfare of Pigs at Slaughter.” EFSA Journal, vol. 18, no. 6, June 2020, https://doi.org/10.2903/j.efsa.2020.6148.
von Wenzlawowicz, M, et al. “Identifying Reasons for Stun Failures in Slaughterhouses for Cattle and Pigs: A Field Study.” Animal Welfare, vol. 21, no. 1, 1 June 2012, pp. 51–60, https://doi.org/10.7120/096272812×13353700593527.
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Thompson et al. (2022) describe the state of current guidelines:
The current recommendations for freestall accommodation space allowances for dairy cattle worldwide have no scientific basis and show great variability; for example total space allowance recommendations range from 6.0 to 11 m² per animal amongst countries worldwide. For context an average adult commercial dairy cow would occupy in the region of 1.8–2 m² when standing.
In practice, the size of housing space likely differs substantially between farms. Indeed, a field study of dairy cows in the UK by Thompson et al. (2020) found large variability in amounts of total space per cow across randomly selected farms:
Large variability was identified between farms in total space available per cow, with a range from 5.4 to 12.7 m² [mean = 8.3 m², median = 8.2 m², interquartile range (IQR) = 1.9 m²]. The mean living space was 2.5 m², with a range of 0.5 m² to 6.4 m² (median = 2.4 m², IQR = 1.6 to 3.2 m²).
In a study of dairy farms in Canada, Charlton et al. (2014) found:
On average, stall width was 116 cm (±5.90 cm; range = 104–137 cm) and average stall length was 240 cm (±17.67 cm; range = 207–314 cm).
Thompson, Jake S., et al. “A Randomised Controlled Trial to Evaluate the Impact of Indoor Living Space on Dairy Cow Production, Reproduction and Behaviour.” Scientific Reports, vol. 12, no. 1, Mar. 2022, https://doi.org/10.1038/s41598-022-07826-9.
Thompson, J.S., et al. “Field Survey to Evaluate Space Allowances for Dairy Cows in Great Britain.” Journal of Dairy Science, vol. 103, no. 4, Apr. 2020, pp. 3745–3759, https://doi.org/10.3168/jds.2019-17004.
Charlton, G. L., et al. “Stocking Density, Milking Duration, and Lying Times of Lactating Cows on Canadian Freestall Dairy Farms.” Journal of Dairy Science, vol. 97, no. 5, May 2014, pp. 2694–700, https://doi.org/10.3168/jds.2013-6923.
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As noted previously, standards for animal welfare are generally higher in the EU than elsewhere in the EU. So, as we did with pigs, we’re going to focus on how cows are treated in the EU — but keep in mind that standards in the rest of the world are likely much worse.The EU represents something like the best case for how almost all cows are treated.
The European Food Safety Authority report on the welfare of dairy cows (Nielsen et al., 2023), notes:
Due to climatic conditions and/or limited availability of pasture, year-round access to pasture is not achievable in most EU countries (Reijs et al., 2013). Exceptions are the Portuguese Azores Islands, with a mild climate all year round (de Almeida et al., 2021), and Ireland, though with a lower proportion of farms. Common in Ireland, however, are pasture-based systems with grazing periods over a large part of the year and shorter periods of winter indoor housing (Crossley et al., 2021).
…The most prevalent housing systems in the EU are cubicle housing systems, followed by open-bedded systems and tie-stalls. The proportion of farms offering access to pasture has declined in several EU MSs in the last decades, with an increasing number of farms converting to zero-grazing systems.
Cows are often kept tethered, either permanently or at least the during winter, in ‘tie-stall’ systems (Nielsen et al., 2023):
Worldwide, tie-stall systems have been the predominant type of housing for dairy cows for decades (EFSA AHAW Panel, 2009a,b). In 2008, the proportion of cows tethered at least temporarily during winter in Europe was estimated to be between 20% in the lowlands and 80% in higher, marginal regions (Veissier et al., 2008).
…In tie-stall systems, animals are tethered while in the barn; however, a distinction can be made between (a) permanent tethering (all year round) and (b) tethering during the winter period combined with a varying degree of access to pasture during the summer (review in Beaver et al., 2021).
…In conventional dairy farming, apart from the general requirements in Council Directive 98/58/EC, there are no specific legal EU regulations/restrictions on tethering, except in individual countries, such as Sweden, where access to pasture must be provided during the summer (Loberg et al., 2004), and where construction of new buildings to tether cows has been prohibited since 2007 (Lundmark Hedman et al., 2018). In Denmark, only tie-stall systems built before 2010 may currently be used.11 A Danish ban on tethering will come into force in 2027 and until then grazing is mandatory in summer in tethered herds (review in Beaver et al., 2021). In Austria,12 permanent tethering is not permitted, but with exemptions in terms of lack of space for loafing areas or safety concerns.
Tethering has important welfare implications (Nielsen et al., 2023):
Important welfare implications of tethering compared to loose housing arise from the restricted freedom of movement (Veissier et al., 2008), which can be associated with an increased prevalence of locomotory disorders (Bielfeldt et al., 2005; Mattiello et al., 2005; Kara et al., 2011; Bouffard et al., 2017), as well as an inability to lie or rest comfortably (Haley et al., 2000; Ostojić Andrić et al., 2011; Popescu et al., 2014), an inability to perform comfort and social behaviour (review in Beaver et al., 2021) and an inability to perform oestrus behaviour. In addition, tethering restricts typical calving behaviour as well as early maternal behaviour.
Nielsen, Søren Saxmose, et al. “Welfare of Dairy Cows.” EFSA Journal, vol. 21, no. 5, 1 May 2023, https://doi.org/10.2903/j.efsa.2023.7993.
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Greenwood, 2021, conducted a review of beef production. Greenwood was a researcher at the Armidale Livestock Industries Centre in New South Wales. He notes:
Beef industries in Europe, New Zealand and India rely heavily on their substantial dairy industries for beef and veal production. Most cow-calf operations within major advanced beef producing regions and countries are pasture-based. South America and Australia have pasture-based systems for growing cattle and finish a substantial proportion of cattle and use pasture for a considerable proportion of cattle for slaughter. North American production systems include a higher proportion of cattle that are feedlot finished for slaughter, although feedlot finishing is increasing in Australia and major South American beef producing nations. … [In Argentina,] feedlot finishing accounted for 28% of cattle slaughtered in 2016 (MLA, 2018a).
…Efficiencies of feedlot production and target market dictate the genotypes of cattle preferred for feedlot finishing. Higher yielding cattle that may be bred from high-yielding terminal-sire European breeds are favoured for efficient, leaner beef production using shorter feedlot finishing periods (≤100 days) to improve consistency of eating quality. Higher-value markets that demand highly marbled beef including export markets to Japan and South Korea require longer-feedlotting periods (100 to ≥350 days, including up to 600 days).
Greenwood, Paul. “Review: An Overview of Beef Production from Pasture and Feedlot Globally, as Demand for Beef and the Need for Sustainable Practices Increase.” Animal, vol. 15, no. 1, 15 July 2021, p. 100295, https://doi.org/10.1016/j.animal.2021.100295.
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According to a scientific opinion from the European Food Safety Authority (Bøtner et al., 2012):
Disbudding means the removal of the horn buds in calves when the actual horn is still absent or very small (< 2 cm), which generally includes animals up to 2 months of age. Only two methods are usually used for disbudding calves – thermocautery (cauterisation with a hot-iron) and chemical cauterisation (caustic paste). The expression dehorning is used for older animals, in which actual horn removal is achieved by means of instruments such as a scoop, embryotomy wire, shears,saws, and others.
On the associated pain (Bøtner et al., 2012):
Dehorning is much more painful that [sic] disbudding. Dehorning, if carried out only under local anaesthesia, will cause severe pain, although this will be slightly delayed in time. Both cautery methods will cause pain for at least 6 hours, but animals disbudded by thermal cautery will struggle more during the procedure. Only nerve blocking with a local anaesthetic associated with a NSAID significantly reduces pain, independently of the method.
On the prevalence of the practice and use of pain relievers (Bøtner et al., 2012):
According to a large European survey carried out in 2008 (ALCASDE, 2009), 40 % of beef farms (which corresponded to approximately 40% of beef cattle) kept bulls without horns. Of this population, 63% were disbudded (52% of these by hot-iron and 48% by caustic paste) and 35% were dehorned. About 2% of the beef cattle population were from polled breeds.
…The ALCASDE (2009) survey showed that anaesthetic or analgesic treatment is administered to the animals prior to or after disbudding in only 35 % of beef cattle. The use of analgesia and sedation increases when dehorning is carried out on older animals (52% of beef), since it is a more invasive procedure and animals are more difficult to restrain. In another European survey it was shown that NSAID were given to 50 % of cows that underwent Caesarean section, 55 % of claw amputations, and in only 1% of dehorning cases (Whay and Huxley, 2005). In another study,1.7 % and 4.6 % of the 605 respondents said they used NSAID after disbudding and castration,respectively.
…A large US survey reported that some dairy owners used an anaesthetic (12.4 %) and analgesia (1.8 %) for dehorning (Fulwider et al.,2008).
…Misch et al. (2007) found that 78 % of dairy producers dehorned their own calves but only 22% used local anaesthetics, and it was also shown that producers who used local anaesthetics were 6.5 times more likely to have veterinary involvement in their dehorning decisions. Horn removal from older cattle was performed with frequent use of drugs and, therefore, it was more consistently carried out by veterinary practitioners, often with the assistance of the stockman.
Bøtner, Anette, et al. “Scientific Opinion on the Welfare of Cattle Kept for Beef Production and the Welfare in Intensive Calf Farming Systems.” EFSA Journal, vol. 10, no. 5, May 2012, p. 2669, https://doi.org/10.2903/j.efsa.2012.2669.
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The European Food Safety Authority report on the welfare of dairy cows (Nielsen et al., 2023) identified mastitis as a substantial welfare concern:
Mastitis is a disease, characterised by inflammation of the mammary gland (De Vliegher et al., 2018) commonly caused by an intramammary infection (IMI), typically bacterial but less commonly also fungal. The pathogens enter the mammary gland via the teat canal. The condition can be divided in a clinical and a subclinical form, despite there is no respective definition of the two types. Clinical mastitis (CM) is associated with clinical signs, such as abnormal milk and swelling of the mammary gland. It represents a painful condition which results in e.g. reduced eating and lying time, altered laterality of lying or restlessness at milking (Siivonen et al., 2011); severe cases of clinical mastitis may also lead to hyperalgesia (Fitzpatrick et al., 1998). Clinical mastitis is thus considered a substantial welfare problem.
Mastitis is common on dairy farms. According to a systematic review and meta-analysis of hundreds of studies worldwide (Krisnamoorthy et al., 2021):
The pooled prevalence of SCM [subclinical mastitis] and CM [clinical mastitis] were 42% [Confidence Interval (CI) 38-45%, Prediction Interval (PI) 10-83%] and 15% [CI 12-19%, PI 1-81%] in the World respectively.
The European Food Safety Authority report on the welfare of dairy cows also identified locomotor disorders (including lameness) as a major welfare concern (Nielsen et al., 2023):
Foot and leg disorders can be divided into claw disorders such as sole ulcer or white line disease and disorders of the limbs (muscles, joints and skin). They are one of the major welfare issues in dairy cows as these disorders are commonly associated with pain (e.g. Brenninkmeyer et al., 2013; Somers and O’Grady, 2015; Burgstaller et al., 2016; Westin et al., 2016a; Führer et al., 2019). Additionally, they are often associated with restriction of the animals’ ability to perform natural behaviours, such as locomotion and feeding. Foot and leg disorders can be associated with decreasing body condition and an increased risk of concurrent disease (review in Alvergnas et al., 2019; Charlton and Rutter, 2017; Huxley, 2013; Kester et al., 2014; Nuss and Weidmann, 2013; Oehm et al., 2019; Olechnowicz and Jaskowski, 2011; Penev et al., 2012).
Lameness is common across multiple housing systems (Nielsen et al., 2023):
The prevalence of lameness reported from studies of different housing systems varied markedly, both within and between housing systems. For example, Katzenberger et al. (2020) found an average of 7.9% lame cows in tie-stall systems, whereas Oehm et al. (2020), Popescu et al. (2014) and Bouffard et al. (2017) found a substantially higher prevalence of over 20% lame cows using the same scoring system (see Appendix D, Table D.1 for an overview of the literature).
…An evaluation of different studies in cubicle systems also revealed a diverse picture (Appendix D, Table D.2). Sjöström et al. (2018) found the average prevalence of lame cows (moderately and severely lame cows lumped together) ranging from 7% in Sweden to 26% in Germany and France. Using the same scoring system (3-point scoring according to Welfare Quality®, 2009), Gieseke et al. (2020) reported that on average 16% of cows in cubicle systems in Germany were severely lame. The highest prevalence was reported by von Keyserlingk et al. (2012); on average, 55% of cows assessed in each herd in the North-East of the USA were lame (score ≥ 3 in a 5-point system) and 8% were scored severely lame (score ≥ 4). The lowest proportions of lame cows among the studies included in this work (6%) were reported from Algerian small-scale farms (Dendani-Chadi et al., 2020).
…In straw yard systems, the proportion of lame cows (including severely lame ones) ranged from 6% in Spain (Sjöström et al., 2018) to 27% in the UK (Barker et al., 2010) (see Appendix D, Table D.3, for an overview of the literature). This range is approximately comparable to that of studies in compost-bedded pack systems (total lameness prevalence from 4% in the US (score ≥ 3; Lobeck et al., 2011) to 25% in Austria (score ≥ 3; Ofner-Schröck et al., 2015), see Appendix D, Table D.4). For pasture-based systems (data recording in summer), a prevalence of 10% and 12% lame cows have been reported by Crossley et al. (2021) and Somers and O’Grady (2015) (Appendix D, Table D.5).
Nielsen, Søren Saxmose, et al. “Welfare of Dairy Cows.” EFSA Journal, vol. 21, no. 5, 1 May 2023, https://doi.org/10.2903/j.efsa.2023.7993.
Krishnamoorthy, Paramanandham, et al. “Global and Countrywide Prevalence of Subclinical and Clinical Mastitis in Dairy Cattle and Buffaloes by Systematic Review and Meta-Analysis.” Research in Veterinary Science, vol. 136, May 2021, pp. 561–86, https://doi.org/10.1016/j.rvsc.2021.04.021.
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According to Weschler, 2023:
In intensive beef production in Europe, finishing beef cattle are typically reared in pens with fully slatted floors and low space allowances… The welfare of finishing bulls and steers is at risk if they are housed on fully slatted concrete or wooden floors or not provided with adequate floor space.
According to a scientific opinion from the European Food Safety Authority (Bøtner et al., 2012):
Beef cattle kept on slatted floors have a higher incidence of injuries than animals on straw or sloped, partially straw-bedded areas.
Multiple studies find that slatted floors lead to lameness (for example, Murphy et al., 1975, Murphy et al., 1987, Brscic et al., 2015, Dewell et al., 2018).
Wechsler, B. “Floor Quality and Space Allowance in Intensive Beef Production: A Review.” Animal Welfare, vol. 20, no. 4, Nov. 2011, pp. 497–503, https://doi.org/10.1017/s0962728600003134.
Bøtner, Anette, et al. “Scientific Opinion on the Welfare of Cattle Kept for Beef Production and the Welfare in Intensive Calf Farming Systems.” EFSA Journal, vol. 10, no. 5, May 2012, p. 2669, https://doi.org/10.2903/j.efsa.2012.2669.
Murphy, PA, et al. “Epiphysitis in Beef Cattle Fattened on Slatted Floors.” PubMed, vol. 97, no. 23, 6 Dec. 1975, pp. 445–7.
Murphy, Peter A, and John Hannan. “Effects of Slatted Flooring on Claw Shape in Intensively Housed Fattening Beef Cattle.” The Bovine Practitioner, 1 Nov. 1987, pp. 133–135, https://doi.org/10.21423/bovine-vol0no22p133-135.
Brscic, M., et al. “Assessment of Welfare of Finishing Beef Cattle Kept on Different Types of Floor after Short- or Long-Term Housing.” Animal, vol. 9, no. 6, 25 Feb. 2015, pp. 1053–1058, [https://doi.org/10.1017/s1751731115000245](https://doi.org/10.1017/s1751731115000245.
Dewell, Reneé D., et al. “Association of Floor Type with Health, Well-Being, and Performance Parameters of Beef Cattle Fed in Indoor Confinement Facilities during the Finishing Phase.” The Bovine Practitioner, American Association of Bovine Practitioners, Feb. 2018, pp. 16–25, https://doi.org/10.21423/bovine-vol52no1p16-25.
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Placzek et al., 2020, conducted a review of separation at birth:
New-born dairy calves are usually permanently separated from their dams within a few hours after birth. This is a typical practice in dairy farming and applies both to organic and conventional production systems (Kälber and Barth 2014). According to the farmers in the study of Wagenaar and Langhout (2007), without early separation, the cows would feed uncontrollable amounts of milk to their calves, which would reduce the amount of produced milk and, consequently, farmers’ income… The reduction of stress is also an argument of the advocates of early cow-calf separation. Supporters of this practice argue that the stress of animals is minimized when the separation takes place before a bond is established between cow and calf (Busch et al. 2017; Ventura et al. 2013).
Both the cows and the calves exhibit behavioral responses after separation that suggest they are experiencing distress (Marchant-Forde et al., 2002):
Early separation in cattle has only received limited attention (Hudson and Mullord, 1977, Kent and Kelly, 1987, Lidfors, 1996, Weary and Chua, 2000, Flower and Weary, 2001) and most of this research has focused on how separation affects the cow, rather than the calf. It has been shown that cows, in particular multiparous cows, find early separation stressful (Phillips, 1993) and that even 24 h after separation cows can still show behavioural signs of distress (Hudson and Mullord, 1977, Kent and Kelly, 1987). However, others report the response to separation being short-lived and mild (Hopster et al., 1995). For the calf, separation prior to natural weaning also appears to evoke increased vocalisation rates, activity and catecholamine concentrations (Lefcourt and Elsasser, 1995; Lidfors, 1996).
Recent studies have investigated the effect of delayed compared to early separation. Some studies conclude that later separation results in more behavioural stress responses in the calves and cows, for example, Flower et al., 2001, find:
The late-separation cows showed a stronger response to separation from the calf than cows separated from calves at less than 1 day after birth. This result corresponds well with earlier studies (Lidfors, 1996; Weary and Chua, 2000) in which separation occurred at the latest 4 days after birth rather than 2 weeks
While others report similar levels of behavioural measures of stress, for example, Mac et al., 2023:
These findings suggest a similar behavioral response to full calf separation and greater occurrence of vocalizations, from cows maintained in a long-term [100 days], pasture-based, cow-calf rearing system when compared to cows separated within 24 h.
Placzek, M., et al. “Public Attitude towards Cow-Calf Separation and Other Common Practices of Calf Rearing in Dairy Farming—a Review.” Organic Agriculture, vol. 11, 8 July 2020, https://doi.org/10.1007/s13165-020-00321-3.
Marchant-Forde, Jeremy N., et al. “Responses of Dairy Cows and Calves to Each Other’s Vocalisations after Early Separation.” Applied Animal Behaviour Science, vol. 78, no. 1, Aug. 2002, pp. 19–28, https://doi.org/10.1016/s0168-1591(02)00082-5. Accessed 30 Jul. 2024.
Flower, Frances C, and Daniel M Weary. “Effects of Early Separation on the Dairy Cow and Calf”: Applied Animal Behaviour Science, vol. 70, no. 4, Jan. 2001, pp. 275–284, https://doi.org/10.1016/s0168-1591(00)00164-7.
Mac, Sarah E, et al. “Behavioral Responses to Cow and Calf Separation: Separation at 1 and 100 Days after Birth.” Animal Bioscience, 14 Nov. 2022, https://doi.org/10.5713/ab.22.0257.
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The British Veterinary Association’s position on surplus male production animals discusses the prevalence of male culling of dairy calves in the UK:
This issue affects large numbers of male dairy calves (bobby calves), which do not have the desired genetic traits for economic meat production and so are often not considered suitable for typical beef rearing. In 2015, 19% of bull calves were killed shortly after birth (approximately 95,000 calves).
We were unable to find rates of culling at birth for other regions, but it’s worth noting that the UK (alongside the EU) tends to have stronger welfare standards than the rest of the world.
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According to the European Food Safety Authority scientific opinion on the welfare of calves (Nielsen et al., 2023):
At ~ 2–5 weeks of age, male calves and some female calves not kept for herd replacement are moved from the dairy farm of origin to auction markets/assembly centres or transported directly to specialised veal units for further fattening (EFSA AHAW Panel, 2022b). Typically, these calves are of Holstein/Friesian breeds, but crossbreds can also be reared as veal calves. In some countries, calves can be, alternatively, fattened in the farm of birth, as it is the case of some herds in France (breeder‐fatteners).
…The diets of calves reared for white veal are restricted in iron to produce meat that is light in colour (hence the name ‘white’ veal) and are comprised mostly of milk replacer, grains and a small amount of roughage (Magrin et al., 2020). Compared with earlier feeding practices, a larger amount of solid feed than what is legally required, has been provided to calves in recent years; however, there is still a tendency to provide solid feed in the form of small particles. Calves are usually fed milk replacer in open troughs or from open buckets without a teat and are not weaned until slaughter. The exact duration of the fattening varies depending on the production country, with France having shorter cycles compared with the Netherlands and Italy (150–175 days vs 190–200 days).
…Compared with white veal, the production of ‘rosé’ veal differs – these calves are weaned off milk at about 3–4 months of age and slaughtered at 8–12 months of age.
…In 2021, ~ 4.08 million white veal calves were slaughtered in the EU‐27 accounting for ~ 620,000 t carcass per year. In addition, ~ 400,000 rosé calves are raised every year (accounting for ~ 76,000 t‐equivalent carcass per year). In 2021, ~ 4.08 million white veal calves were slaughtered in the EU‐27 accounting for ~ 620,000 t carcass per year. In addition, ~ 400,000 rosé calves are raised every year (accounting for ~ 76,000 t‐equivalent carcass per year).
The European Food Safety Authority describes the typical lives of calves raised for veals (Nielsen et al., 2023):
Calves fattened for veal are transported to the veal farm at ~ 14–35 days of age (for details on the impact on welfare of transport of unweaned calves please refer to EFSA AHAW Panel, 2022b). At arrival, calves are placed in individual pens within a large pen, using removable barriers made from tubular metal bars (Figures 5 and and6).6). These individual pens must by law at least be as wide as the height of the calf at the withers and as long as the length of the calf multiplied by 1.1, according to the Council Directive 2008/119/EC. This phase may last between 3 and 6 weeks.
The report identified restriction of movement, isolation stress, inability to perform suckling behaviour, inability to perform play and exploratory behaviour, prolonged hunger, resting problems, gastroenteric disorders, respiratory disorders, as welfare concerns during this stage.
Following the individual pen stage (Nielsen et al., 2023):
Calves are released into group pens holding typically 5–7 calves, but in some instances up to 10 animals are kept together. In group pens, full social contact with pen mates is possible. Calves are kept in this system from 4–7 weeks of age until slaughter at 21–28 weeks. In France, holdings tend to have shorter cycles (160–165 days) in France compared with Italy, Germany and the Netherlands (190–200 days). Calves reared for veal are typically provided with the minimum EU space allowance per animal (i.e. 1.8 m2 per calf) and housed on slatted floors made of wood or very rarely concrete, though rubber flooring on top of wooden or concrete slats is also used on some farms. No enrichment is provided.
Outside of the EU, conditions are much worse, but have recently seen some improvement (Creusinger et al. 2021):
Housing at calf raising facilities, particularly within the veal industry, has been criticized by the public [e.g., (47)] and animal welfare groups. It is commonplace to house calves individually with limited space for the first 8 weeks following arrival to calf raisers. Individual housing of calves is used [as] a biosecurity measure to prevent respiratory disease [reviewed by (48)], which is a leading cause of morbidity and mortality in veal calves (49). However, the potential health benefits of individual housing are inconclusive as prolonged individual housing in veal facilities (>4 weeks) is a risk factor for nasal discharge and coughing (50). Furthermore, individual housing profoundly limits calves’ ability to perform natural behaviors, such as play or social grooming (51, 52). Overall, housing calves in social isolation negatively impacts their physiology, behavior, and welfare [reviewed by (48)] likely due to the lack of both physical and social stimulation. A lack of stimulation may result in boredom and lead to the development of abnormal behaviors (53). In addition to socially restricted housing environment, access to the outdoors or pasture, under most circumstances, is not provided.
…In some parts of the U.S. and Canada, public scrutiny has resulted in regulation and policies that impact how calves are housed and raised. For example, group housing after weaning and increased space allowance per calf is required in Canada and by the Veal Quality Assurance program in the U.S., as well as specific state legislation. For example, veal calves raised in California must have enough room to stand up, lie down, fully extend their limbs, and turn around freely.
We’d guess that conditions outside North America and the EU tend to be similar to those in the US without state-specific legislation, but we haven’t investigated this guess.
Nielsen, Søren Saxmose, et al. “Welfare of Calves.” EFSA Journal, vol. 21, no. 3, Mar. 2023, https://doi.org/10.2903/j.efsa.2023.7896.
Creutzinger, Katherine, et al. “Perspectives on the Management of Surplus Dairy Calves in the United States and Canada.” Frontiers in Veterinary Science, vol. 8, 13 Apr. 2021, https://doi.org/10.3389/fvets.2021.661453.
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The European Food Safety Authority report on the welfare of cattle during transport (Nielsen et al., 2022):
In total, 11 welfare consequences were identified as being highly relevant for the welfare of cattle during transport based on severity, duration and frequency of occurrence. These were (i) group stress, (ii) handling stress, (iii) heat stress, (iv) injuries, (v) motion stress, (vi) prolonged hunger, (vii) prolonged thirst, (viii) respiratory disorders, (ix) restriction of movement, (x) resting problems and (xi) sensory overstimulation. The occurrence of each type of welfare consequence varied depending on the stage and means of transport.
…In Europe, the current dairy cow population has been estimated to be approximately 23 million animals (Augère-Granier, 2018). Overall, the annual culling rate is 25–30% (Nor et al., 2014). This means, that annually at least 5 million dairy cows are transported to slaughter by road (Figure 15).
…As most cull dairy cows are not in prime condition, there are additional challenges faced by cull dairy cows that are more severe than those experienced by many beef cattle, and the animals will often be less able to cope with the stressors associated with transport (Cockram, 2021) than the average animal.
The European Food Safety Authority report on the welfare of cattle at slaughter gives additional detail (Nielsen et al., 2020).
During transport, cattle are at risk of heat and cold stress, prolonged thirst, prolonged hunger, and fatigue:
During transport, before arriving at slaughter, animals may face very adverse climatic conditions. A Canadian study on 6,152 long journeys from Alberta to the US showed that ambient temperatures across all journeys ranged from –42 to 45°C with a mean value of 18 ± 11.8°C, while temperature variation within a journey was from 0 to 46°C with a mean value of 15 ± 6.6°C (González et al., 2012).
…In very large countries such as Australia (Fisher et al., 2009) or Canada (Gonzales et al., 2012), transport duration and water deprivation for 30 h or 48 h have been reported. Hogan et al., 2007 estimated that in Australia cattle are frequently subjected to feed and water deprivation for about 12 h before, and then during transport in order to reduce digesta load in the gastrointestinal tract. In the latter study, food and water deprivation was associated with some stress indicated by increased levels of plasma cortisol that may be partly responsible for an observed increase in the output of water and nitrogen in urine and faeces.
In certain parts of the world, fasting in cattle can start a few days before transport (Warriss et al., 1990), since it takes time to empty the digestive tract in ruminants, but this is not a common practice worldwide. Smith et al. (1982) in Australia made an experiment on 144 steers fasting them 53 h pre-slaughter and submitting them to 0, 3 or 12 h of road transportation. The mean rate of live weight loss declined progressively with fasting time, from 2.57 kg/h during the first 5.3 h to 0.71 kg/h during the final 23.6 h, meaning that live weight is mainly decreasing at the beginning of fasting, when the digestive tract is emptying. Over the first 18–24 h of transport, loss of bodyweight can reach up to 11%. Animals that lost more than 10% of their bodyweight during transport had a greater likelihood of dying or becoming non-ambulatory or lame (González et al., 2012) thus indicating a compromised welfare.
Long waiting times upon arrival before unloading continue the welfare consequences of transport. In addition, long-waiting times can result in aggressive interactions between cattle:
During transport, cattle usually try to maintain their balance standing up while the vehicle is moving. When the vehicle is stationary, for example at arrival, the animals may start moving (Knowles, 1999), and it is very likely that aggressive interactions would be detrimental to welfare if the cattle are mixed groups of bulls, or cows and heifers in oestrus (Kenny and Tarrant, 1987a,b).
…In an observational survey in a French slaughterhouse during two periods of 5 days (Bourguet et al., 2010), the average time between arrival and unloading was 5.6 ± 0.9 min. Other cattle transport surveys reported by Faucitano and Perdenera (2016) revealed average waiting times between arrival and unloading of 20–30 min, with maximum waiting time ranging from 3 h to overnight. Indeed, in a study of González et al. (2012) in cattle transported for long hauls (> 400 km) from Alberta (Canada) to the US, out of 6,152 journeys studied 82.5% of trucks were not unloaded immediately with a mean unloading delay of 39 min and a maximum of 12 h.
Nielsen, Søren Saxmose, et al. “Welfare of Cattle during Transport.” EFSA Journal, vol. 20, no. 9, 7 Sept. 2022, p. e07442, https://doi.org/10.2903/j.efsa.2022.7442.
Nielsen, Søren Saxmose, et al. “Welfare of Cattle at Slaughter.” EFSA Journal, vol. 18, no. 11, Nov. 2020, https://doi.org/10.2903/j.efsa.2020.6275.
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The European Food Safety Authority summarises the welfare concerns at all stages of the slaughter process for cattle in their report on the welfare of cattle at slaughter (Nielsen et al., 2020).
During unloading:
It is considered inappropriate handling causing fear and/or pain when staff move single animals since cattle are gregarious; force the cattle to get off from the truck too quickly or through non-adapted bridges and raceways; or use the wrong material (e.g. goads instead of flags). The use of electric goads causes pain and leads to aversion (Pajor et al., 2000) and is considered a serious welfare concern. Inappropriate handling might cause animals rushing and getting scared and then slipping and falling during unloading. If animals are running, they are more likely to slip and fall (Sandstrom, 2009). It may also lead to animals being reluctant to move, freezing or turning back which in turn may provoke using force and harsh methods (e.g. with electric goads).
Lairage (i.e. holding pens prior to slaughter) can lead to social stress, fear and pain due to unexpected loud noises, thermal stress :
Conflict with pen mates as well the inability for subordinate animals to escape the dominant ones can lead to fear. In case of social stress, animals can be bruised, injured and suffer from pain. Continuous fights can lead to resting problems within the group and fatigue.
…Steers, heifers and anoestrous cows are not aggressive in lairage. Bulls on the other hand need to be managed carefully. Young bulls in a familiar group exhibit play mounting, whereas in mixed groups the interaction between them is of agonistic nature, including butting, mounting, pushing and chasing others. These behaviours can continue for up to 12 h and even in the darkness at night (Kenny and Tarrant, 1987a,b). Owing to this, young bulls in a mixed group are prone to pain, fear and fatigue.
…Noise levels in a slaughterhouse, especially in lairages where metallic gates and ventilation fans are used and pressure washing equipment may be operated, can have a significant effect on the welfare of cattle (Grandin, 1998b). In an exhausted individual, the compensatory mechanisms are more vulnerable than in a rested individual (Brouček, 2014). Thresholds for discomfort for cattle was noted at 90–100 dB, with physical damage to the ear occurring at 110 dB (Phillips, 2009).
…Dairy breeds are more sensitive to noise than beef breeds (Lanier et al., 2000). Weeks et al. (2009) measured the average noise value during the 24 hr in 34 abattoirs in England and Wales and recorded values from 52 to 79 dB for cattle lairages. Iulietto et al. (2018) used a mobile phone app to record noise levels in cattle lairages in three Italian slaughterhouses and reported a range of average values of 56–101 dB.
Loading for stunning:
The movement from the lairage pen to the stunning area constitutes one of the key points regarding animal welfare in abattoirs. Handling and moving of cattle from lairage pens to the restraint should be done calmly and without the use of force by a person. In abattoirs with high slaughter throughput, most of the time animals are forced to move quickly during the last meters prior to stunning to maintain the throughput rate.
…Many stunning boxes have design faults that contribute to levels of distress in cattle (FAWC, 2003). Stepped or sloped floor surfaces are built to assist with roll-out of unconscious cattle from the stun box, which may cause animals to panic.
Stunning methods:
Mechanical stunning methods: Mechanical stunning methods induce brain concussion resulting in unconsciousness through the impact of a penetrative captive bolt, a non-penetrative captive bolt, or free projectiles on the skull of the animal.
…Electrical stunning methods: The principle of electrical stunning is the application of sufficient current through the brain to induce generalised epileptiform activity in the brain, so that the animal becomes immediately unconscious (head-only electrical stunning, Section 3.2.1.5). Head-only electrical stunning can be performed in combination with or immediately followed by passing an electrical current through the body to generate fibrillation of the heart or cardiac arrest (head-to-body electrical stunning, Section 3.2.5.2).
…[During stunning], cattle might experience pain and fear during restraint. Pain and fear can also be caused by ineffective stunning, which will lead to persistence of consciousness during hoisting, sticking and bleeding. Furthermore, recovery of consciousness might occur in effectively stunned animals if sticking was delayed or was not properly done.
…To prevent pain, mechanical restraint should suit the size of the animal. Most of the restraints used in cattle slaughterhouses are not adjustable.
…Penetrative captive bolt powered by cartridge or compressed air is the most commonly used method to stun cattle. Death may occur depending on the degree of injury to the brain but is not a guaranteed outcome (Lambooij and Algers, 2016). Therefore, captive bolt stunning shall be followed as quickly as possible by bleeding or destruction of the brain and upper spinal cord by pithing.
Stunning failures:
Fries et al. (2012) investigated the efficacy of captive bolt stunning in two cattle head deboning slaughterhouses, where a total of 8,879 cattle skulls were investigated for number and precision of shots. Overall, 64.7% of the skulls in slaughterhouse 1 and 65.3% in slaughterhouse 2 were shot in the ideal position and direction. A medium precision (i.e. shots within a range of a maximum distance of 3.0 to 4.5 cm from the crossing point and/or a maximum deviation of 10° to 20° from the vertical direction) was observed in 31.3% and 31.5% of cases, while 4.0% and 3.1% of the skulls indicated a poor precision. In both plants, skulls with more than one shot hole were observed.
Slaughter:
Exsanguination of cattle immediately following stunning is an important step in the slaughter process intended to [cause] death in unconscious animals. Under commercial slaughter situations, cattle are bled out with a chest stick (referred to as sticking) aimed at severing the brachiocephalic trunk which gives rise to the carotid arteries and vertebral artery supplying oxygenated blood to the brain (EFSA, 2004; HSA, 2016a,b).
…The presence of consciousness at sticking or cutting, or recovery of consciousness during bleeding, is a serious animal welfare concern for at least two reasons. First, the incision made in the neck and chest sticking involves substantial tissue damage in areas well supplied with nociceptors (Kavaliers, 1988). The activation of the protective nociceptive system induces the animal to experience pain. Second, onset of death due to sticking is not immediate, and there is a period of time during which the animal may regain consciousness and then experience pain, fear and distress (EFSA AHAW Panel, 2013).
…In effectively stunned cattle, sticking should be performed as soon as possible. In any case a maximum stun-to-stick interval of 60 seconds for the penetrative captive-bolt and 30 seconds for the non-penetrative captive-bolt have been suggested (HSA, 2016a,b). In commercial slaughterhouses, sticking of cattle may be performed after captive bolt stunning, which is most commonly used, following shackling and hoisting the unconscious animals and moving it on an overhead rail to the bleeding area. Owing to this, there would be a delay between the end of stunning and sticking.
…Cattle with signs of life undergoing dressing may recover consciousness and consequently experience pain, fear and distress. Lack of skilled operators, short bleeding time, incomplete sectioning of the brachiocephalic trunk or carotid arteries, occlusion of carotids (false aneurisms) and lack of monitoring of death before dressing begins are hazard origins.
Slaughter without stunning:
When slaughtered without stunning, cattle are killed through exsanguination by severing all the soft tissues, including blood vessels, in the neck usually at the level of second to fourth cervical vertebrae (EFSA, 2004; von Holleben et al., 2010).
…Cattle are either restrained in an upright, rotated or inverted position. For example, in Europe, from the 2.1 million animals slaughtered without stunning, more than 1.6 million (78%) are slaughtered in a rotating device, while the rest (22%) are slaughtered in an upright device…
…The presence of consciousness during slaughter without stunning causes severe welfare consequences. First, the incision made in the neck and chest sticking involves substantial tissue damage in areas well supplied with nociceptors (Kavaliers, 1988). The activation of the protective nociceptive system induces the animal to experience pain. Second, onset of death due to sticking is not immediate, and there is a period of time during which the animal remains conscious and experiences pain, fear and distress (EFSA AHAW Panel, 2013).
Nielsen, Søren Saxmose, et al. “Welfare of Cattle at Slaughter.” EFSA Journal, vol. 18, no. 11, Nov. 2020, https://doi.org/10.2903/j.efsa.2020.6275.
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Both castration and tail docking are allowed to be performed on sheep without analgesics or anaesthesia before a certain age, usually seven days old for tail docking of lambs and six weeks to three months for castration (some methods always require pain relief) in most parts of the world.
Madeleine, et al., discuss tail docking around the world:
Docking the tails of sheep is a very common animal husbandry practice, particularly in countries that manage sheep in extensive systems such as Australia… The prevention of flystrike (cutaneous myiasis) and breech cleanliness are the primary reasons producers dock sheep tails in Australia and around the world. Flystrike is a significant welfare issue and an Australian priority endemic disease, costing the industry AUD 300 million in treatment, prevention, and production losses annually. (Woodruff et al., 2023)
According to a report into castration and tail docking in lambs by the UK Government’s Animal Welfare Committee:
The evidence presented by the industry indicates that castration is usually carried out using the rubber ring method without anaesthesia or analgesia. Other options for castration include short scrotum castration, clamp castration and the combined method, although the evidence suggests that these are less widely used than rubber rings. Tail docking may also be carried out using the rubber ring method, or with a sharp knife, using a hot iron that cauterises the wound, or with a clamp (e.g., Burdizzo), generally combined with a rubber ring. As with castration, the most common method is the rubber ring on young lambs without anaesthesia or analgesia.
On the use of anaesthesia, the report notes:
…In 2008, FAWC recommended that pain relief (anaesthetics and analgesics) should be used for both castration and tail docking whenever possible, and that research should be directed towards the development of practical methods for delivering pain relief under farming conditions and for different ages of lambs.
Industry evidence suggests that pain relief is rarely used for either castration or tail docking. There are several likely reasons for this. There is no legal requirement to use anaesthetics on lambs that are castrated or tail docked using a rubber ring within their first 7 days of life. However, as noted above, anecdotal evidence suggests that these practices are often carried out after the 7-day legal limit for using rubber rings (or, in Scotland, for using rubber rings without anaesthetic).
A more probable explanation is that use of anaesthetics would be an additional stage in the process, thus adding stress for the lamb, and extra time and cost for the farmer during the very busy lambing period. Farmers may not identify signs of pain or discomfort or may choose to overlook these and may well lack the skills required to administer a local anaesthetic by injection in a consistently hygienic and effective way.
The 2008 FAWC (UK Government Farm Animal Welfare Committee) report referenced in the first line described the causes of pain in detail:
Elastration is probably the most widely used method of tail docking. The ring prevents
blood flow to the distal tissues, which atrophy and drop off after 4 to 6 weeks. The method is
quick, easy, and reliably effective, but has been shown to cause acute pain and stress in lambs at all ages investigated including lambs of less than one week of age, for which its use without anaesthesia is restricted by law in the UK. Although there have been fewer studies of tail docking compared with those of castration, particularly with regard to age effects, there is no evidence to indicate that the pain response in lambs docked below one week is less than that for animals docked at older ages. By comparison with castration using rubber rings, however, cortisol responses indicate that the pain and stress are less severe when rings are applied to the tail. Nevertheless, the pain may still be considerable and, as with castration, it has been noted that in very young lambs the level of acute pain may be severe enough to prevent the animals from ingesting protective amounts of colostrum.
in the UK, rules on castration in goats appear seem to be similar to those for sheep:
Under the Protection of Animals Acts 1911 to 1988 (in Scotland, the Protection of Animals (Scotland) Act 1912 to 1988), it is an offence to castrate a goat, which has reached the age of 2 months without the use of an anaesthetic. Furthermore the use of a rubber ring or other device to restrict the flow of blood to the scrotum is only permitted without an anaesthetic if the device is applied during the first week of life. Under the Veterinary Surgeons Act 1966, as amended, only a veterinary surgeon or veterinary practitioner may castrate a goat after it has reached the age of 2 months.
As we’ve noted previously, the UK and the EU tend to have higher animal welfare standards than the rest of the world, so we’d guess this represents some of the best treatment for sheep and goats globally.
Woodruff, Madeleine, et al. “Measuring Sheep Tails: A Preliminary Study Using Length (Mm), Vulva Cover Assessment, and Number of Tail Joints.” Animals, vol. 13, no. 6, 7 Mar. 2023, p. 963, https://doi.org/10.3390/ani13060963.
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As with cows, disbudding means removing horn buds in kids when the horn is absent or very small (up to around 2 months of age).
The UK Government’s Code of recommendations for the welfare of livestock: goats notes:
Disbudding and dehorning. These operations must be carried out by a veterinary surgeon. If disbudding is to be carried out, this should be done at the earliest possible age; 2 to 3 days is ideal but not later than 10 days. Dehorning an adult goat is a stressful procedure and should be avoided… Under the Veterinary Surgeons Act 1966, as amended, only a veterinary surgeon or veterinary practitioner may… dehorn or disbud a goat, except the trimming of the insensitive tip of an ingrowing horn which, if left untreated, could cause pain or distress.
This suggests that it’s legal (and likely common) to disbud goat kids.
Singh et al., 2024, discuss this further:
Goat kids, particularly females from milking herds, are commonly subjected to disbudding to reduce potential injury to animals and humans from horns or entanglement in equipment in the milking shed. Goat kids are typically disbudded within the first week of life, most commonly via thermal cauterization using a hot iron. Hot iron disbudding is a painful procedure that requires pain relief to be provided to the animals undergoing this procedure to avoid a negative impact on their welfare. Hot iron disbudding is considered a significant surgical process and should be performed by a veterinarian or under their supervision. This is particularly important in goat kids because there is a significant risk of thermal brain damage and death.
…The pain from hot iron disbudding has at least two phases, which probably require different approaches to alleviation. The application of a hot iron causes intense acute pain, and then, the release of inflammatory mediators from the burnt tissue will cause a lower-grade but longer-lasting pain.
…The United Kingdom and several European countries mandate that disbudding in goats is exclusively carried out by a veterinarian, utilizing appropriate anesthetics and analgesics [6]. Consequently, in New Zealand and Australia, a significant shift has occurred, and pain relief measures have become mandatory for disbudding goat kids [13]. This represents a noteworthy advancement in animal welfare practices.
This strongly suggests that such steps have not been made elsewhere in the world, and disbudding often occurs without anaesthesia.
Singh, Preet, et al. “Pain Mitigation Strategies for Disbudding in Goat Kids.” Animals, vol. 14, no. 4, Jan. 2024, p. 555, https://doi.org/10.3390/ani14040555. Accessed 25 Mar. 2024.
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According to a scientific opinion from the European Food Safety Authority (Berg, et al., 2014):
[T]he legs and the feet are the parts of the body that are most frequently injured in sheep. These injuries interfere with normal behaviour and locomotion, and may have a debilitating effect by preventing the animal from feeding normally. This aspect is particularly relevant in sheep as most of the farms present pasture based management systems. Sheep often graze low-quality upland pastures, thus they have to walk long distances to gain access to a sufficient amount of food.
Lameness is the most common sign of limb injury, which compromises the animals’ welfare by causing long-term pain and impairing normal sheep behaviour. The vast majority of lameness cases can be attributed to scald, also known as interdigital dermatitis (IDD; infection with Fusobacterium necrophorum, a naturally occurring environmental pathogen, particularly on wet pasture), and foot-rot (infection with Dichelobacter nodosus). Foot-rot may follow an initial inter-digital infection and can be classified as benign, if lesions are limited to the inter-digital space with little involvement of the horn, or virulent if extensive separation of horn from deeper structures occurs (Winter, 2008).
Winter, 2004, found:
Lameness remains one of the most important welfare issues affecting the sheep industry. Recent estimates suggest that over 80 per cent of flocks contain lame sheep, with a prevalence in some flocks of over 9 per cent for footrot and over 15 per cent for scald.
We’re not sure of the source of those estimates — from context, they appear to be talking about the UK.
There’s no EU scientific opinion on goats, so it’s harder to find reliable information.
Footrot also occurs in goats — as can be seen from industry sources discussing the issue, although it’s unclear how common this is.
Jacques et al., 2023, find lameness rates for goats between 5% and 20% in New Zealand:
Severely lame goats (score 4) in seasonal and extended lactation produced 7.05% and 8.67% less milk than goats not lame, respectively. When the prevalence of severe lameness is between 5 and 20% of the herd, the estimated average daily milk income lost was between NZD 19.5 and 104 per day.
Hill et al., 1997, find lameness rates of 2.6 to 24.4% in the UK:
In the first population-based study of lameness and foot lesions in adult goats in the UK, a random sample of 307 adult goats from four large commercial dairy farms was examined. The overall proportion of lame goats was 9.1 per cent (2.6 to 24.4 per cent). The abnormalities detected were horn separation (29.6 per cent), white line lesions (13.0 per cent) slippering (10.1 per cent), abscess of the sole (4.2 per cent), foreign body, and granulomatous lesions (1.0 per cent). Between 83.1 and 95.5 per cent of the goats had overgrown horn on at least one foot.
Mathhews, 2016, notes:
In goats, pain is recognised as one of the main signs associated with most lesions of the feet, so lameness in goats is a welfare issue and can be a particular problem where routine foot care is neglected. The chronic pain state associated with lameness can be associated with significant production losses – reduced milk yield and growth impairment – because of the inability/unwillingness to feed.
Charlotte, Berg, et al. “Scientific Opinion on the Welfare Risks Related to the Farming of Sheep for Wool, Meat and Milk Production.” EFSA Journal, vol. 12, no. 12, Dec. 2014, https://doi.org/10.2903/j.efsa.2014.3933.
Winter, A. “Lameness in Sheep 1. Diagnosis.” In Practice, vol. 26, no. 2, 1 Feb. 2004, pp. 58–63, https://doi.org/10.1136/inpract.26.2.58.
Jaques, Natasha, et al. “The Effect of Lameness on Milk Production of Dairy Goats.” Animals, vol. 13, no. 11, Jan. 2023, p. 1728, https://doi.org/10.3390/ani13111728.
Hill, N. P., et al. “Lameness and Foot Lesions in Adult British Dairy Goats.” Veterinary Record, vol. 141, no. 16, Oct. 1997, pp. 412–416, https://doi.org/10.1136/vr.141.16.412.
Matthews, John. “Lameness in Adult Goats.” Diseases of the Goat, John Wiley & Sons, Ltd, 19 Aug. 2016, pp. 81–104, doi.org/10.1002/9781119073543.
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According to a scientific opinion from the European Food Safety Authority (Berg, et al., 2014):
Dairy ewes are at risk of developing production-related diseases such as mastitis. The incidence of clinical intra-mammary infections in sheep is relatively low, at or below 5 % (Kilgour et al., 2008). However, the incidence of sub-clinical mastitis varies from 4 % to more than 40 %… The udder of ewes with acute mastitis may be discoloured and dark,swollen, very warm and in severe cases can evolve to gangrenous mastitis with toxaemia and loss of condition while the gangrenous tissue can necrotise, causing the loss of part of the udder and leave a large granulating wound characterised by secondary bacterial infections. Gangrenous mastitis can sporadically cause death of ewes but it always represents a relevant welfare concern.
The major welfare concern is acute (clinical) mastitis rather than sub-clinical mastitis, which refers to infection without substantial discolouring or swelling of the mammary gland.
We’re uncertain about the exact prevalence in goats, but industry sources report it as a similar issue to mastitis in sheep –— for example, an article from the Cornell College of Veterinary Medicine notes:
Mastitis is one of the more common health problems affecting sheep and goats. Severe cases can result in death of the ewe, but more often it takes its toll in the form of treatment costs, premature culling, and reduced performance of lambs and kids.
Charlotte, Berg, et al. “Scientific Opinion on the Welfare Risks Related to the Farming of Sheep for Wool, Meat and Milk Production.” EFSA Journal, vol. 12, no. 12, Dec. 2014, https://doi.org/10.2903/j.efsa.2014.3933.
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According to a scientific opinion from the European Food Safety Authority (Berg, et al., 2014):
Lamb mortality is a significant welfare concern; the average mortality in developed countries is 15-20%, with nearly 50 % of these lamb deaths occurring within the first three days of life. The main causes of lamb deaths are: 1) pre- or peri-parturient disorders (30-40 %); 2) weakly lamb/exposure/starvation(25-30 %); 3) infectious disease and gastro-intestinal problems (20-25 %); 4) congenital disorders (5-8%); 5) predation, misadventure and unknown causes (5 %) (Roger, 2008). The risks of lamb succumbing to any of the causes of death will vary somewhat by management. For example, outdoor lambing systems may have higher deaths from dystocia (as the risks of a ewe experiencing difficulties and not being assisted are greater) and exposure/starvation, whereas indoor lambing systems face greater risks of infectious diseases and abortions.
Charlotte, Berg, et al. “Scientific Opinion on the Welfare Risks Related to the Farming of Sheep for Wool, Meat and Milk Production.” EFSA Journal, vol. 12, no. 12, Dec. 2014, https://doi.org/10.2903/j.efsa.2014.3933.
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According to a scientific opinion from the European Food Safety Authority (Berg, et al., 2014):
Exclusive attachments between ewe and lambs form immediately after birth and ewe and lambs are rarely separated for long in a natural situation, and never in a threatening situation, until at least six months after birth (Arnoldet al., 1979). Therefore, separation of ewe and lambs may engender similar anxiety reactions to social isolation (Napolitano et al., 2008). For ewes, these attachments generally wane within a few days of separation, in line with the reduction in a lactation response. In lambs, the timing of separation from the ewe is likely to be important, affecting whether the lamb is able to form effective relationships with others (e.g. human caregivers, peers), although separated lambs rarely perform as well as lambs raised by their mothers (Snowder and Knight, 1995; Binns et al., 2002; Dwyer, 2008). Abrupt weaning is also associated with elevated plasma cortisol (Mears and Brown, 1997; Rhind et al., 1998; Orgeur et al., 1999), depressed growth rates (Jagusch et al., 1977; Watson, 1991; Napolitano et al., 1995) and increased susceptibility to disease (Jagusch et al., 1977; Watson 1991). (EFSA, 2014)
Napolitano, et al., 2008, found:
When artificial rearing is applied lambs are often kept with mothers for 2 days to allow the ingestion of maternal colostrum and then abruptly removed from their dams… These animals when exposed to open field tests show reduced levels of vocalization, are slower to initiate movements, spend less time in ambulatory behaviour and display an increased cortisol response than non-separated animals… Early weaned lambs emit an increased number of high pitched bleats immediately after weaning than before and this increment is still evident 2 days afterwards. Neither partial nor gradual separation from mothers is able to reduce the stress associated with early weaning. In conclusion, premature separation from mothers has clear and marked detrimental effects on various functions in lambs. For lambs maternal deprivation seems to be worse at 2 days (artificial rearing) than at 3 months of age (early weaning).
Separation appears to be a pretty much universal procedure — it’s referenced in industry documents and we couldn’t see any sources from industry claiming not to separate lambs from ewes.
Napolitano, Fabio, et al. “Welfare Implications of Artificial Rearing and Early Weaning in Sheep.” Applied Animal Behaviour Science, vol. 110, no. 1-2, Mar. 2008, pp. 58–72, https://doi.org/10.1016/j.applanim.2007.03.020.
Charlotte, Berg, et al. “Scientific Opinion on the Welfare Risks Related to the Farming of Sheep for Wool, Meat and Milk Production.” EFSA Journal, vol. 12, no. 12, Dec. 2014, https://doi.org/10.2903/j.efsa.2014.3933.
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The European Food Safety Authority report on welfare of sheep and goats at slaughter (Nielsen et al., 2021):
During transport, before arriving at slaughter, animals may face very adverse climatic conditions. When arriving at slaughter, waiting times in a stationary vehicle may expose animals to thermal stress (heat or cold stress) depending on the external climatic conditions as well as on the variation in the internal truck environment and on the welfare state of the animals.
…Sheep attempt to maintain their balance independently and do not lean against each other during road transportation, and a lack of space makes it difficult for them to do this (SCAHAW, 2002). It has been suggested that high stocking densities can become hazardous because, in addition to causing thermal stress, they prevent sheep from making adjustments to their posture and position to maintain their balance in a moving vehicle (Knowles, 1998; Knowles et al., 1998). It has been reported that all the sheep lie down after about 4 h of transport given a space allowance equivalent to a k-value of 0.026 (Knowles et al., 1995; Cockram et al., 1996), which is very similar to a k-value of 0.027 for a lying sheep suggested by Baxter (1992). It has been reported that sheep lie down in increasing numbers in the first 5–10 h and tend to get up if the vehicle stops during long distance road transport in Europe (Knowles, 1998).
…Small ruminant can be subjected to prolonged hunger since they are deprived from food for the time feed is removed on farm until their arrival on the slaughterhouse. Usually, feed is not provided to sheep and goats during transport… Sheep are frequently subjected to feed deprivation for about 12 h before, and then during, transport and feed may be provided later in lairage… Sheep are frequently subjected to water deprivation for about 12 h before, and then during transport. In the EU, they might be subjected to water deprivation for a maximum of 8 h (Reg 1/2005). Extensively reared sheep in some countries may have to travel for thousands of km before reaching slaughterhouses (Hogan et al., 2007; Gallo et al., 2018).
We couldn’t find good data on the prevalence of these conditions, but due to the lack of regulation — and the clear cost of providing food, water, controlled temperatures, and space — we’d expect such poor conditions to be common. As one quantitative measure, the report notes that 1 in 10,000 lambs die on the journey:
The incidence of dead on arrival (DOA) can be used as the ultimate welfare outcome to assess the cumulative effects of on-farm handling and transport. Knowles et al. (1994a) reported a mortality of 0.007% in lambs transported directly from farm to slaughter (62 miles) in the south of England and 0.031% in those going through the auction market (199 miles). In Chile, mortalities of 0.1–0.13% have been reported at arrival of commercial loads of lambs at the slaughterhouses. These higher mortalities are associated with stressful procedures of rounding up in the fields, walking long distances to reach loading pens on the farm, longer distances (and time) travelled by the lambs, the low space allowances, bad roads, use of inadequate vehicles and untrained handlers (Gallo et al., 2018).
Nielsen, Søren Saxmose, et al. “Welfare of Sheep and Goats at Slaughter.” EFSA Journal, vol. 19, no. 11, Nov. 2021, https://doi.org/10.2903/j.efsa.2021.6882. Accessed 9 Dec. 2021.
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The European Food Safety Authority report on the welfare of sheep and goats during slaughter suggest that stunning methods commonly fail to induce sustained unconsciousness during the bleeding phase of slaughter (Nielsen et al., 2021):
The main stunning methods employed in the slaughter of sheep and goats are grouped into mechanical and electrical methods.
Mechanical stunning methods induce brain concussion resulting in unconsciousness through the impact of a penetrative captive bolt, a non-penetrative captive bolt,percussive blow to the head or ﬁrearms with free projectiles on the skull of the animal. Electrical stunning methods: The principle of electrical stunning is the application of sufﬁcientcurrent through the brain to induce generalised epileptiform activity in the brain, so that the animal becomes immediately unconscious (head-only electrical stunning 3.2.2.1). Head-only electrical stunning can be performed in combination with or immediately followed by passing an electrical current through the body to induce ﬁbrillation of the heart or cardiac arrest (head-to-body stunning 3.2.2.2)
…Pain and fear can also be caused by ineffective stunning, which will lead to persistence of consciousness during shackling, hoisting, and bleeding. Furthermore, recovery of consciousness might occur in effectively stunned animals if bleeding was delayed or was not properly carried out, i.e. blood vessels supplying oxygenated blood to the brain are not completely cut or bleeding was impeded.
…Manual application of head-only electrical stunning of animals in a group situation may be difﬁcultas animals, especially sheep, tend to group together and goats being more agile might jump if not properly restrained. They hide their heads under each other. As a result, application of the tongs can be difﬁcult, which can lead to misplacement of the stunning tongs or pre-stun shocks. This means that the lack of restraint can be a hazard for poor application of the stunning method. Excessive pressure applied to sheep and goats during mechanical restraint could lead to pain and fear. Restraining goats in V-type restraint designed for sheep can be problematic, when the restraint device cannot be adjusted to the size of the goats. Stunning animals when crowded in a group increases the risk of the animal close to the one being stunned receiving electric shocks, leading to pain and fear… Berg et al. (2012) reported that 33% of lambs that were judged to be ineffectively stunned had incorrect stunning tong placements.
The overall prevalence of failed stunning is unclear — but we’d be surprised if rates were much lower than 10% (as we found above that 10% or more cattle and pigs go through a failed stun).
The report notes that not all sheep and goat are stunned:
Animals may be hoisted and suspended from an overhead rail with a shackle attached to one or both of the hind legs for the purpose of slaughter without stunning. Hoisting live and conscious sheep and goat upside down for the purpose of slaughter without stunning was common in some countries (Velarde et al., 2014).
…Velarde et al. (2014) also reported that 60% of sheep that were hoisted and 67% of sheep that were rotated and restrained on their side struggled, suggesting pain, fear and/or distress.
…Barrasso et al. (2020) reported that 16 out of 120 sheep subjected to slaughter without stunning showed signs of consciousness, i.e. positive corneal reﬂex (4) or rhythmic breathing (12) at 90 s after neck cutting. Four animals subjected to head-only electrical stunning followed by slaughter also showed rhythmic breathing at 90 s post cut.
Finally, the report notes:
During all phases of the slaughter process, sheep and goats may experience negative welfare consequences such as: heat stress, cold stress, fatigue, prolonged thirst, prolonged hunger, impeded movement, restriction of movements, resting problems, social stress, pain, fear and distress.
Nielsen, Søren Saxmose, et al. “Welfare of Sheep and Goats at Slaughter.” EFSA Journal, vol. 19, no. 11, Nov. 2021, https://doi.org/10.2903/j.efsa.2021.6882. Accessed 9 Dec. 2021.
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Saraiva et al., 2022, reviewed the literature on stocking density, and found that:
There is a large body of scientific literature indicating negative effects at different densities in different species, life-stages and production systems. For example, Atlantic salmon (Salmo salar) smolts and post-smolts reared in tanks at densities of 15 kg/m3 presented increased skin and fin damage, lower growth, and higher incidence of agonistic behaviors (6), whereas high stocking densities (35 kg/m3) also led to increased skin and fin damage. In land-based systems, negative effects on food conversion rate (FCR) and physiological stress markers on Atlantic salmon occur at densities above 75 Kg/m3 (7). Crowding can also result in aggression, physical damage, and deterioration of water quality (6, 8). Densities above 26.5 kg/m3 cause decreased growth rate, feed intake and feed utilization in adult Atlantic salmon in sea cages (7). For rainbow trout (Oncorhynchus mykiss), the average food consumption of individual fish was found to decrease with increasing density (2, 9). On the other hand, low density resulted in poor feeding response causing mortality through excessive aggressive behavior in this species (2), and both low and high stocking densities of rainbow trout parr and smolts have negative effects on welfare (10).
Saraiva, J. L., et al. “Finding the ‘Golden Stocking Density’: A Balance between Fish Welfare and Farmers’ Perspectives.” Frontiers in Veterinary Science, vol. 9, July 2022, https://doi.org/10.3389/fvets.2022.930221.
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For example, Gradall et al., 1982, found:
Creek chubs preferred highly turbid water (56.6 formazin turbidity units—FTU) over moderately turbid water (5.8 FTU) but brook trout did not show a preference. In moderately turbid water, both species were more active, and used overhead cover less, than in clear water.
Gradall, Kenneth S., and William A. Swenson. “Responses of Brook Trout and Creek Chubs to Turbidity.” Transactions of the American Fisheries Society, vol. 111, no. 3, May 1982, pp. 392–395, https://doi.org/10.1577/1548-8659(1982)111%3C392:robtac%3E2.0.co;2.
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According to estimates of the global amount of farmed fishes killed for food in Mood et al., the countries accounting for 70% of farmed fish volume have no welfare protections for fish:
Many of the top producing countries have some general animal welfare law that, in principle, covers farmed fishes at slaughter but very few have fish-specific welfare requirements (Table 4). The key results from the analysis of law (Table S8 of the supplementary material) are that:
- At least ten countries have no such legal protection, accounting for 70% of the total estimate by mid-point;
- In at least 15 countries, including the UK and together with the EU27, fishes have some stated general protection, either specifically or as vertebrates or living creatures, which is usually a requirement not to cause unnecessary suffering. These account for 28% of the total estimate by mid-point.
- Of these 15, three countries have fish-specific slaughter codes that require stunning and/or prohibit certain inhumane slaughter methods. These three countries account for 0.2% of the total estimate by mid-point.
- Countries that were not analysed accounted for 3% of the total estimate by mid-point.
Mood, Alison, et al. “Estimating Global Numbers of Farmed Fishes Killed for Food Annually from 1990 to 2019.” Animal Welfare, vol. 32, 2023, https://doi.org/10.1017/awf.2023.4.
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Based on numbers from Šimčikas. The upper estimate of one trillion fish is based on some sources which suggest a large number of juvenile fish raised in China for an unknown reason — and assuming that this unknown reason is to deal with a high pre-slaughter mortality rate. Šimčikas notes that he’s uncertain about the sources and about whether this could be explained by a high pre-slaughter mortality rate. Overall, we’d guess that the lower end of the estimate seems more likely to be correct.
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The UK Government’s Farm Animal Welfare Committee opinion on the welfare of farmed fish notes:
There is increasing understanding of the factors most important to fish
welfare, primary among which is water quality. This has many components, including concentrations of necessities such as oxygen and harmful solutes, and factors such as pH and temperature. Many of these components are interdependent, with optimal ranges affecting each other and also varying between species of fish.
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The UK Government’s Farm Animal Welfare Committee opinion on the welfare of farmed fish notes:
While biosecurity has generally improved, disease and parasites are still major problems and are considered the greatest fish welfare problems by some. Effective treatments are lacking for some diseases (see Appendix 4), while for other diseases treatments are aversive, have significant side effects or are limited in their use by environmental controls. In some cases disease is increased by poor husbandry and environment because stress compromises the immune system.
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The UK Government’s Farm Animal Welfare Committee opinion on the welfare of farmed fish notes:
Sea lice are a variable but still sometimes major concern in salmon production and welfare; in 2013 the SSPO started to publish a quarterly report on prevalence of sea lice and on the management strategies undertaken.
The use of wrasse to prevent sea-lice is a welfare concern in itself. The opinion continues:
While wrasse are not farmed for human consumption, use of this and other species as ‘cleaner-fish’ to alleviate sea lice infections in farmed salmon seawater operations is increasing. Numbers of captive wrasse are increasing and are predicted to exceed 2 million per year within the next three years. Welfare issues include capture from the wild (which also raises questions of sustainability), predation by salmon, especially during feed withdrawal, and the lack of refuges.
For more, see this blog post on the welfare issues surrounding cleaner fish.
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The UK Government’s Farm Animal Welfare Committee opinion on the welfare of farmed fish notes:
Feed is withdrawn before handling and transport to reduce metabolism (and hence ill-effects of stress), oxygen demand and defaecation. This improves water quality during crowding and transport, and food hygiene during post slaughter processing… Sudden feed withdrawal may reduce welfare because aggression may increase… Feed restriction is sometimes practised for management purposes, for example to slow the growth of some fish to meet a required delivery date.
Martins, et al., 2011, summarises findings on aggression in fish and relates them to limits in resources:
Fish in a natural environment can live alone or in groups (Brännäs et al. 2001). Group living can take the form of short-term aggregations or be more long term and highly structured (Pitcher and Parrish 1993; Grant 1997; Hoare and Krause 2003). Group living confers advantages in foraging, resource defence and predator detection (Pitcher et al. 1982; Ryer and Olla 1991, 1992; Pitcher and Parrish 1993), and shoaling is one of the most common social fish behaviours (Pitcher and Parrish 1993; Parrish et al. 2002; Hoare and Krause 2003). However, when resources or the number or territories are limited, group living becomes a disadvantage as competition for the resource increases (Pitcher and Parrish 1993). Limiting resources may lead to the emergence of competitive behaviours, which may take the form of dominance rank-based hierarchies (Jobling 1983; Jobling and Koskela 1996). This kind of hierarchy is generally established after agonistic encounters between two individuals, and the rank within the hierarchy depends on their ability to fight (Huntingford and Turner 1987).
…A subordinate position within a group or social hierarchy may be a stressor (Schreck 1981). A subordinate individual can be subject to social stress resulting from attacks and repeated threats of attack from more dominant individuals for access to resources (food, sexual partners and territory). Social stress leads to marked behavioural and physiological changes in subordinates, who often show a general behavioural inhibition of food intake, aggressiveness, locomotory activity, changes in skin colorations and higher levels of plasma cortisol (Denight and Ward 1982; O’Connor et al. 1999; Winberg and Nilsson 1993a, b; Øverli et al. 1998). It is, however, notable that cortisol elevation can also occur in dominant fish within minutes of the end of aggressive encounters (Øverli et al. 1999).
Fin erosion appears to be a particularly prevalent form of injury (McLean et al., 2024):
Fin erosion is considered an important welfare issue in fish since caudal, dorsal, and pectoral fins are nociceptive. The causes of fin erosion, which can achieve a prevalence of 60–90%+ [63,69–71], appear diverse [68,72–75] but, unlike fin rot, it is not due to bacterial infection.
Martins, Catarina I. M., et al. “Behavioural Indicators of Welfare in Farmed Fish.” Fish Physiology and Biochemistry, vol. 38, no. 1, 28 July 2011, pp. 17–41, https://doi.org/10.1007/s10695-011-9518-8.
McLean, Ewen, et al. “The Impact of Marine Resource-Free Diets on Quality Attributes of Atlantic Salmon.” Fishes, vol. 9, no. 1, 17 Jan. 2024, pp. 37–37, https://doi.org/10.3390/fishes9010037.
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Cannibalism is a major problem among aggressive, predatory fish (Naumowicz, et al., 2017):
Cannibalism in cultured fish occurs in different age groups and its type and development depend mostly on the species and production technology. It represents a major problem in the commercial production of many fish species (especially predatory species) and ranges from 15% to over 90% of individuals (Hecht and Appelbaum 1988). This phenomenon is mainly observed in fish from the following families: airbreathing catfish (Clariidae), pikes (Esocidae), percids (Percidae), characids (Characidae), latids (Latidae), gadids (Gadidae) and in over 30 other families, including cyprinids (Cyprinidae) and salmonids (Salmonidae), (Smith and Reay 1991; Hecht and Pienaar 1993; Qin et al. 2004).
…Intracohort cannibalism is typical of farming conditions and is divided into two types: type I, the so called ”early” type, which occurs in the larval phase and is independent of a diversity in fish sizes, where the victim is not completely ingested or consumed; and type II, a later form associated with heterogeneous growth, when the victim is consumed whole (Hecht and Appelbaum 1988; Smith and Reay 1991; Baras and Jobling 2002).
…The outcomes of these two types of cannibalism differ in the level of mortality. In the case of type I, it ranges between 1.5 and 12.0% of the initial stock of European perch (Perca fluviatilis) larvae (Baras et al. 2003; Babiak et al. 2004; Król and Zieliński 2015) and from 10 to 17% in the stock of pikeperch (Sander lucioperca) larvae (Zakęś and Demska-Zakęś 1996; Zakęś 2012; Król and Zakęś 2016) or even 40% in dorada (Brycon moorei) (Baras et al. 2000b). Type II usually generates significantly higher losses and is mainly reported in a stock characterised by a large heterogeneity in size (Kro´l and Zielin´ski 2015).
Naumowicz, Karolina, et al. “Intracohort Cannibalism and Methods for Its Mitigation in Cultured Freshwater Fish.” Reviews in Fish Biology and Fisheries, vol. 27, no. 1, 18 Jan. 2017, pp. 193–208, https://doi.org/10.1007/s11160-017-9465-2.
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Note we are referring to the mandarin fish Siniperca chuatsi, a popular food fish in China – not the unrelated mandarinfish Synchiropus splendidus, commonly found in saltwater aquariums.
According to Fishcount’s fish counts by species (which are taken from production data from FishStat, a database by the Food and Agriculture Organization of the United Nations — and then combined with estimates of the mean weight of each species), around 2,600,000 tonnes of salmon, 340,000 tonnes of mandarin fish, and 37,000 tonnes of tuna were in global aquaculture in 2017.
They estimated this means slaughter of 280 million to 650 million salmon and around 670 million mandarin fish.
It’s worth nothing that many other fish are carnivorous but eat small animals, such as zooplankton, insects, and the larvae of larger animals.
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A scientific opinion from the European Food Safety Authority concluded that the most commonly used methods for fish slaughter are not humane and very likely result in extended periods of suffering (Blokhuis et al., 2004):
Many existing commercial killing methods expose fish to substantial suffering over a prolonged period of time. For some species, existing methods, whilst capable of killing fish humanely, aren’t doing so because operators don’t have the knowledge to evaluate them… Fish find CO₂ narcosis very aversive. It can be a stunning or a stun / killing method. But in commercial practice, it is usually a sedation method only because of the short exposure time used… Asphyxia, asphyxia in ice / thermal shock, salt bath, ammonia solution, electro-immobilisation /electrostimulation / physical exhaustion using electrical shocks, decapitation and bleeding out /exsanguination are not humane methods for killing fish.
In practice, a recent study of the practices in 67 slaughter facilities in Italy (accounting for 41% of the total volume of fish slaughtered in Italy per year) reported that more than half do not stun fish prior to slaughter, although it is technically required by EU law (Clemente et al., 2023):
According to the European legislation on the slaughter of farmed species (EC Reg. 1099/2009) and the recommendations of the WOAH and EFSA, animals must be subjected to a stunning process before being slaughtered in order to become unconscious and insensible. However, based on the results of the survey, in Italy, more than half of the fish-slaughter facilities (35/64) practiced the asphyxia in air or the thermal shock method. These procedures are considered non-humane methods of slaughtering fish by WOAH and EFSA. In fact, the asphyxia in air is considered only as a ‘killing’ method; the thermal shock does not stun the fish but produces only sedation, leading the conscious animal to death by asphyxia (12, 20).
As with other animals, we’d expect that the welfare of farmed fish is worse outside the EU.
Blokhuis, Harry J., et al. “Opinion of the Scientific Panel on Animal Health and Welfare (AHAW) on a Request from the Commission Related to Welfare Aspects of the Main Systems of Stunning and Killing the Main Commercial Species of Animals.” EFSA Journal, vol. 2, no. 7, July 2004, p. 45, https://doi.org/10.2903/j.efsa.2004.45.
Gianfilippo Alessio Clemente, et al. “Farmed Fish Welfare during Slaughter in Italy: Survey on Stunning and Killing Methods and Indicators of Unconsciousness.” Frontiers in Veterinary Science, vol. 10, Frontiers Media, Oct. 2023, https://doi.org/10.3389/fvets.2023.1253151.
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From a literature review by Yue, 2014, which goes into more detail than the European Food Safety Authority cited above:
Asphyxiation in air involves the removal of fish from water, whereby the animals suffocate and die. This method is extremely aversive to fish, who often show violent escape behaviors accompanied by maximum stress responses.⁴⁹ When fish are taken out of water, their gills collapse, preventing oxygen exchange with their environment.⁵⁰ The time to death in air is affected by the ambient temperature; for example, rainbow trout die after 2.6 minutes at 20ºC (68ºF), 3 minutes at 14ºC (57.2ºF), and 9.6 minutes at 2ºC (35.6ºF). As fish are poikilotherms, animals whose body temperature fluctuates according to the temperature of the environment, reducing the temperature of their bodies typically prolongs the time to anoxia (a condition in which the tissues of the body do not receive adequate amounts of oxygen) and, therefore, the time to insensibility, lengthening the period of distress or suffering.⁵¹
We haven’t individually investigated the sources used in this review, so there’s a reasonable chance we shouldn’t trust these results much.
Yue, Stephanie. “The Welfare of Farmed Fish at Slaughter.” Impacts on Farm Animals, no. 3, 2014, www.wellbeingintlstudiesrepository.org/hsus_reps_impacts_on_animals/3/.
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From a literature review by Yue, 2014, which goes into more detail than the European Food Safety Authority cited above:
Similar to the method of asphyxiation on ice, live chilling involves immersing fish in chilled water, with the intentions of causing fish either to become torpid (motionless) or stunned before slaughter.^54,55 This method of cooling muscles immobilizes the animals so they can be more easily handled.⁵⁶ However, cold shock is unacceptable as it prolongs the period of consciousness (i.e., the time to unconsciousness increases with decreasing temperatures)⁵⁷ and does not reduce the animals’ ability to feel pain.⁵⁸ Fish may be exposed to water of approximately 1ºC (33.8ºF) or colder.^59,60 The chilled water often causes the fish to become sedated⁶¹ or immobile, but may not render them insensible to pain and the effects are reversible if transferred back to normal water temperatures.⁶²
…A research team led by Bjorn Roth from the University of Bergen, Norway, observed chilled fish exhibiting non-uniform behavior upon exit of the chilling tank. Although some fish were motionless, others showed degrees of physical activity, and all showed signs of consciousness including eye-rolling and respiratory activity upon removal from the chilling tank, as well as immediate responses such as writhing and thrashing during gillcutting for exsanguination. The team concluded that live chilling followed by exsanguination of fish appears to be highly stressful and should not be practiced as the animals are not properly stunned.⁶⁸
We haven’t individually investigated the sources used in this review, so there’s a reasonable chance we shouldn’t trust these results much.
Yue, Stephanie. “The Welfare of Farmed Fish at Slaughter.” Impacts on Farm Animals, no. 3, 2014, www.wellbeingintlstudiesrepository.org/hsus_reps_impacts_on_animals/3/.
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From a literature review by Yue, 2014, which goes into more detail than the European Food Safety Authority cited above:
Commonly used as a stunning method, water saturation with carbon dioxide creates an acidic and hypoxic environment that eventually leads to narcosis. In response to this treatment, fish have been reported to show aversive behavior and flight reactions.^70,71,72,73 During the initial period of narcosis, fish exhibit intensely aversive behavior for a minimum of approximately 30 seconds.⁷⁴ Robb et al. reported that salmon react with behavior including vigorous head and tail shaking for approximately 2 minutes after being immersed in carbon dioxide-saturated water although some salmon have been recorded to show this aversive behavior for up to 9 minutes.⁷⁵ It has been reported that the high amount of activity seen during carbon-dioxide stunning routinely causes gill hemorrhaging.⁷⁶
In addition to these behavioral responses, some fish such as rainbow trout, carp, and eels also increase mucus production, a possible sign of stress,^77,78 during carbon-dioxide narcosis.⁷⁹In some cases, it has been observed that fish will demonstrate a “coughing” response as a means to clear excess mucus from their gills.⁸⁰Loss of brain function by this method has been found to take 4.7 minutes for trout⁸¹ and 6.1 minutes for salmon.⁸²
Although considered an unacceptable method of slaughter by the HSA, if carbon-dioxide stunning is used, wellrun systems leave fish in carbon dioxide-saturated water for a minimum of ten minutes in order to induce unconsciousness.⁸³
Despite this, however, it has been reported that fish are customarily removed once movement stops, typically after 2-3 minutes.⁸⁴Thus, there is a concern that fish may be rendered immobile by the carbon dioxide before completely losing consciousness and may be bled or eviscerated while still sensible.^85,86
Aversive behavior to carbon-dioxide stunning has been reported to cause injury and scale loss, and there is no evidence proving that carbon dioxide has any analgesic or anaesthetic effects other than narcosis, which does not imply any reduction in pain or fear.⁸⁷
We haven’t individually investigated the sources used in this review, so there’s a reasonable chance we shouldn’t trust these results much.
Yue, Stephanie. “The Welfare of Farmed Fish at Slaughter.” Impacts on Farm Animals, no. 3, 2014, www.wellbeingintlstudiesrepository.org/hsus_reps_impacts_on_animals/3/.
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From a literature review by Yue, 2014, which goes into more detail than the European Food Safety Authority cited above:
This method typically entails removing fully conscious fish from water, manually restraining them, inserting a sharp knife under their operculae, and severing all four gill arches on one side of their head.⁹⁷ Alternatively, the heart may be pierced, isthmus cut with a knife or the blood vessels in the tail severed.⁹⁸ Fish reportedly struggle intensely for an average of four minutes during this process;⁹⁹ Lambooij et al. found that catfish responded to noxious stimuli for a minimum of 15 minutes after gill-cutting.¹⁰⁰ The Scientific Panel of Animal Health and Welfare of the European Food Safety Authority and others have stated that exsanguination without stunning is inhumane and should not be used for slaughter.^101,102 Although this method has been used commercially in the United Kingdom and in Norway,¹⁰³ behavioral and brain function measures have indeed shown that it is a slow method of slaughter as fish are not rendered immediately insensible.¹⁰⁴
We haven’t individually investigated the sources used in this review, so there’s a reasonable chance we shouldn’t trust these results much.
Yue, Stephanie. “The Welfare of Farmed Fish at Slaughter.” Impacts on Farm Animals, no. 3, 2014, www.wellbeingintlstudiesrepository.org/hsus_reps_impacts_on_animals/3/.
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According to the Food and Agriculture Organization of the United Nations page on American bullfrogs (likely the most common species of farmed frog, the recommended stocking density is 50/m².
Le et al., 2023, surveyed 40 frog farmers farmers in Vietnam — Vietnam is the world’s second-largest frog producer. They found:
Stocking density is high with 146.3±92.3 individuals/m² for production frogs and 51.6±35.7 individuals/m² for breeding frogs… The diseases occurred in tadpole and froglet phase (2-30 days), including septicemia diseases (57.5%), red thighs (45%), white bodies (35%), blindness (35%), digestive disorders (20%), and flatulence (15%). The disease causes were mainly due to poor water quality, weather change, feed, and high stocking density.
According to a veterinary manual:
The first signs that owners often notice about amphibians with septicemia is lethargy or anorexia (lack of appetite). These general signs mean the amphibian is just not feeling well. Other common signs are a red to pink skin color on pale areas of the body, especially the chin, throat, gills, ventral skin, thighs and webs of the feet and toes, swelling of the whole body of fluid accumulation under the skin, making them look bloated; a weird but not uncommon sign is then the amphibian’s stomach comes out of the mouth (it can go back in and the amphibian will be fine); twitching of the limbs or toes, convulsions, paralysis and sudden death also occur in amphibians with septicemia.
American bullfrogs are around 9–15cm long. Assuming they are circular, that’s an area of 0.025 to 0.071 m², meaning around 14–40 bullfrogs could fit in the same square metre without being on top of each other. That’s much less than the 50–200 suggested in the sources above.
Zhao et al., 2019, conducted experiments into the stocking density for Chinese soft-shelled turtles that maximises yield. They found:
The yield of turtles increased gradually with increasing stocking density until reaching 10 turtles/m2.
Chinese softshell turtles reach around 20cm in length at maturity, so they probably have an area of around 0.13 m ² (assuming they’re circular). So 10 turtles would not fit in a single square metre without being on top of each other. We haven’t found a source looking at stocking density in farms, but we’d be surprised if they are not optimising for yield (especially since most Chinese softshell turtles are farmed in China, and China tends to have highly relaxed animal welfare regulation).
Li et al., 2008, discuss white-spot disease of Chinese soft-shelled turtles. They find:
Chinese soft-shelled turtles (Trionyx sinens) in culture farms using an artificial warming system in Zhejiang, China, often show typical signs of white-spot disease such as white spots on their bodies, skin lesions, anorexia and eventually death… The disease often occurs in turtles weighing 5~80 g in culture farms with high population density particularly under fluctuating temperature conditions. It is likely that the turtle’s immune functions were compromised due to temperature fluctuations and high density. In practice, it is difficult for the farmers to keep the water temperature constant via artificial heating systems. The farmers are also not willing to reduce the density of turtle populations for their pursuit of economic benefits.
Le, Diem Kieu, et al. “Production Techniques and Environmental Management in Frog Farming in Dong Thap Province.” Dong Thap University Journal of Science, vol. 12, no. 5, 24 July 2023, pp. 71–77, https://doi.org/10.52714/dthu.12.5.2023.1074.
Jing, Zhao, et al. “Effects of Stocking Density of Chinese Soft-Shelled Turtle and Interactions between Cultivated Species on Growth Performance and the Environment in a Turtle–Rice Coculture System.” Journal of the World Aquaculture Society, vol. 51, no. 3, pp. 788–803, https://doi.org/10.1111/jwas.12665.
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According to Alves, et al., 2022:
Stunning before slaughter should promote the induction and permanence of the animals in a state of unconsciousness to avoid or minimize stress. In bullfrog (Lithobates catesbeianus) slaughter the most used stunning methods are thermonarcosis and electronarcosis… A completely randomized design was conducted with four treatments: electronarcosis stunning (4 s inductive shock, 45.5 v and 10 A electrical current with resistive filter), thermonarcosis (saline solution and ice for 15 min, approximately 1 °C), frogs in control condition of their holding pen and frogs restrained in bag (animals placed in a raffia bag for a period of 1 h:30 min).
According to animal activists, “standard practice for the removal of frogs’ legs is by cutting the legs off with knives, scissors, or simple dismemberment by hand — all while fully conscious,” but we couldn’t find corroborating evidence for these claims.
We couldn’t find any evidence about turtle slaughter, other than this article about turtles in Asian markets in San Francisco, which notes:
The animal advocates insist they are just trying to make the markets obey the same animal-cruelty laws that everyone else follows, regardless of cultural heritage. “My personal feeling is that the cruelty-to-animals law is being violated all the time,” says Richard Schulke, director of SF’s Animal Control and Welfare.
…Michael Lau, a spokesman for Chinatown’s Sun Duck market, describes the standard way to kill a turtle: “First we try to get it to stick its head out, and then when it does, we chop it off right there and then. But if we can’t, we’ll break the shell and then take his head off, which usually takes a minute and a half.” Schulke said a turtle’s head can live for an hour after being severed, exacerbating the cruelty when the head isn’t killed directly with a brain pith. It’s grisly, but experts like the University of California-Davis’s Joy Mench say there’s no better way.
‘De-carapacing’ refers to this practice of removing a turtle’s shell.
Adriana Xavier Alves, et al. “Stunning Bullfrogs by Electronarcosis and Thermonarcosis: Hematological and Plasma Biochemical Responses.” Aquaculture, vol. 548, 1 Feb. 2022, pp. 737545–737545, https://doi.org/10.1016/j.aquaculture.2021.737545.
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Rethink Priorities’ report on farmed shrimp welfare describes the effect of poor water quality on shrimp mortality:
Water quality during preparation for transportation worsens due to disruption of the benthic environment. Catching shrimp using a net “requires that farm personnel walk in the pond, which results in a high degree of sediment suspension that may foul gills and cause undue stress to the juveniles” (Villalón, 1991, p.41). Similarly, Ohs et al. (2007) note that the last shrimp who are transferred by pumping may have “prolonged exposure to concentrated sediments.” These issues could affect any shrimp being transferred between earthen ponds.
During transportation itself, water quality issues arise due to a buildup of ammonia and consumption of dissolved oxygen. Huang et al., (2023) found that after a simulated 72-hour transportation, survival rates for P. vannamei shrimp were 65% when no water was exchanged, and 94% when water was exchanged, and that levels of un-ionized ammonia were significantly higher in the no-water-exchange group.
Farmers normally have an incentive to keep water quality acceptable during transportation. A partial exception comes from Debnath et al. (2016; see also Meshram et al., 2009, p. 186), who note that competition for wild-sourced broodstock supply among hatcheries allows trawlers to lower their transportation standards:
[W]ater is no longer aerated using compressed oxygen during transportation of broodstock to hatcheries after landing. This was a common practice in the past, but is no longer followed widely as lack of aeration does not result in immediate mortality. This has led poorly educated hatchery staff to believe that oxygenation makes little difference to broodstock condition, while in fact, failure to oxygenate water during transport is likely to place additional stress on recently captured broodstock (p. 4)
The report also discusses disease:
Annually, viral infections are responsible for substantial losses in tropical shrimp aquaculture production, and disease is persistently identified by shrimp farmers as the biggest industry challenge (Anderson et al., 2016a; 2016b; 2017; 2018; 2019; HATCH, 2019c; Stentiford et al., 2012). The large burden of disease partly reflects the fact that disease is a downstream consequence of many of the other welfare issues we will discuss in subsequent sections.
The report notes 10 diseases that affect farmed shrimp — symptoms include spots, lethargy, body deformities, changes in colour, reduced food intake and death.
Uawisetwathana et al., 2011 discuss eyestalk ablation:
Eyestalk ablation has been employed to induce reproductive maturation in crustacean [1]. While the ablation can induce ovarian maturation, it also jeopardizes growth, shortens molting cycle, increases energetic demands [2], and resulting in an eventual loss in egg quality and high mortality [3].
This practice is described as standard operating procedure according to technical guidelines for shrimp hatcheries in Latin America created by the Food and Agriculture Organization of the United Nations.
Rethink Priorities’ report on farmed shrimp welfare describes the evidence that this procedure is painful for shrimp:
After having one eyestalk ablated, shrimp display several behaviors potentially indicative of pain, like tail-flicking (see Box 2), recoiling, stooping (lying prone on the pond floor), disorientation-indicative behaviors, avoiding shelter, erratic swimming, and rubbing the affected area for a period of time after ablation (Barr et al., 2008; Diarte-Plata et al., 2012; Taylor et al., 2004).
Welfare considerations for farmed shrimp. Rethink Priorities, 13 Dec. 2023,
Slaughter methods:
According to a fact sheet by the Food and Authority Administration of the United Nations:
After sorting, shrimp are washed, weighed and immediately killed in iced water at 0–4 °C.
However, in the process of ‘harvesting,’ shrimp may be put into large sacks with no ice, leading to deaths by crushing as discussed in the Rethink Priorities report on shrimp welfare:
In the first video linked above (watch from 7:12) they are stored in overcrowded sacks with no ice. Shrimp Welfare Project (2022, p.15) observed shrimp “being crushed both by other shrimp and by workers (who step on the shrimp when placing another net full of shrimp into remaining crates).”
Uawisetwathana, Umaporn, et al. “Insights into Eyestalk Ablation Mechanism to Induce Ovarian Maturation in the Black Tiger Shrimp.” PLoS ONE, edited by Irina Agoulnik, vol. 6, no. 9, Sept. 2011, p. e24427, https://doi.org/10.1371/journal.pone.0024427.
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These welfare concerns are set out in Snails used for human consumption: the case of meat and slime by Daniela Waldhorn, a researcher at rethink priorities.
She writes:
Density and restrictions on movement: Snails reared in farms may suffer from overcrowding, which in turn inhibits snail growth, maturity, fertility and reproduction rate (Cobbinah et al., 2008; Daguzan et al., 1981; FAO, 2013; Thompson & Cheney, 2008). Moreover, high population densities increase the risk of diseases (Cobbinah et al., 2008; Daguzan et al., 1981; FAO, 2013), and hence, snail mortality raises (Daguzan et al., 1981; Daguzan et al., 1985; Dan & Bailey, 1982; Jess & Marks, 1995; Thompson & Cheney, 2008). Images from intensive farms suggest that snails have limited space to move around (see e.g., Cañas, 2018; Iglesias & Castillejo, n.d.).
…Diseases and parasites: Snails can suffer various infectious diseases, but probably the most harmful are epizootic6 diseases. These pathologies are usually related to bacterial agents (Padilla & Cuesta, 2003: 102; Raut, 2004: 599-611). In general, these diseases can quickly appear and decimate farmed snail populations–around 70-80% of individuals (Padilla & Cuesta, 2003: 102). In these facilities, diseases are often caused by poor farm maintenance or abrupt environmental changes (i.e., in humidity or temperature) (Cuéllar et al., 1986).
…Mortality rates: According to Padilla & Cuesta (2003), in an extensive farm, around 20% of newborn snails die during their first few days of life (99). I was unable to find equivalent estimates for other breeding systems. During the growing and fattening phases, different sources estimate that between 10% to 28% of snails usually die (Cuéllar et al., 1986: 123; Daguzan et al., 1985; Dupont-Nivet et al., 2000; Padilla & Cuesta, 2003: 99). In a mixed system, at different density levels, a mortality rate of up to 69% can be expected (Daguzan et al., 1985). Several studies claim that mortality rates increase in overcrowded facilities (Dan & Bailey, 1982; Dupont-Nivet et al., 2000; Jess & Marks, 1995). Additionally, mortality rates among breeding snails seem to be higher. According to different sources, at least 21% and up to 70% of breeding snails typically die (Cuéllar et al., 1986: 123; Daguzan et al., 1981; Daguzan et al., 1985).
…Typically, only adult snails are harvested, either in farms or when snails are collected from the wild (Iglesias & Castillejo, n.d.). Images suggest that snails are collected manually and stored in sacks (see fig. 2) After collection, snails are purged of anything unhealthy they may have eaten. Traditionally, purging involves a period of fasting of five or six days. (Thompson & Cheney, 2008). Afterward, snails are packed together, and practically impeded of all movement.
…For shipping–whether for processing or direct commercialization–snails are packed in containers (e.g., into sacks in plastic crates). Several pictures regularly show snails packed in sacks in overcrowded conditions, crushing each other (see e.g. Touchstone Snail, 2015a).
…Typically, snails are slaughtered by boiling. First, the animals are washed and soaked in water. Then, snails are put in boiling water and cooked to death (Thompson & Cheney. 2008). Discussing whether snails are sentient is beyond the scope of this report. However, it is worthwhile to consider that *Helicidae( snails do display avoidance behavior in response to high temperatures (see Balaban, 2002, and Ierusalimsky & Balaban, 2007 in Crook & Walters, 2011).
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The issues surrounding insect welfare were investigated in a series of papers by Meghan Barrett — who we also interviewed on our podcast.
Barrett et al., 2023, notes:
Stocking density can have multifaceted effects on animal welfare. Beyond direct effects of the proximity of so many animals (e.g. facilitating disease transmission or increased physical contact), too high densities can contribute to inadequate resource availability or accessibility and/or result in behavioral/physiological changes that negatively affect welfare.
When comparing the welfare of insects to vertebrate livestock, it is frequently suggested that rearing insects at high densities in intensive production systems is not likely to be detrimental to their welfare because insects are often found in nature at high densities (e.g. Dossey et al., 2021; Erens et al., 2012; IPIFF, 2019; and see discussion of this issue in Delvendahl et al., 2022). First, it should be noted that natural conditions do not necessarily serve as a guide to high animal welfare. High densities in natural conditions may simply result from overutilization of scarce resources, not because insects’ welfare is better under those conditions.
Second, it should be noted that almost no studies have documented the density of insects in natural conditions nor the prevalence of these densities in natural conditions (where we may also expect a bias towards the documentation of larger/high density populations that are easier to detect, as discussed in studies of other group-living animals: Markham et al., 2015; Sharman and Dunbar, 1982). It is thus unclear what density insect producers should mimic, even if mimicking natural conditions was expected to produce the best outcome for welfare.
Finally, studies that robustly test the hypothesis that high density conditions improve, or harm, wild insect welfare are non-existent. However, high density conditions can substantially increase mortality due to density-dependent factors (e.g. risks of some diseases, resource scarcity, etc.; Lack, 1954). It is important to be critical of the claim that insect welfare is always improved under high density conditions until empirical evidence establishes the appropriate rearing densities for each species’ welfare.
On black soldier flies density (Barrett et al., 2022):
Approximately 40,000 larvae are given 1 m2 space, distributed across several pans, for a density of ~4 larvae/ cm2 (Dortsman et al., 2017).
On cricket density (Rowe et al., 2024):
Reported rearing densities vary greatly. In the USA, some reports have placed cricket nymph densities at 0.04-0.07 crickets /cm2 using stacked egg cartons (Cortes Ortiz et al., 2016); rearing densities can be read as number of crickets per amount of surface area provided for crickets to rest via egg cartons and flooring, and are thus not volumetric. Other US consultancies report densities of 0.4-2.6 crickets/cm2 (Big Cricket Solutions, 2019b), or recommend 1 cricket/20 cm3 or ¹⁄₂.5 cm2 (Orinda et al., 2021). Big Cricket Farms (now Big Cricket Solutions) have self-reported using troughs with 3,000 crickets each (a population density of 1.35 crickets/cm2, according to their unit dimensions and yields). They report that this high stocking density can generate poor welfare conditions for the crickets: “They’ll find a way to escape, they’ll bite each other, they’ll eat each other” (Wiedemann, 2014). Medium-sized A. domesticus farms have an average density of approximately 6,000-12,000 crickets/m2 (0.6-1.2 crickets/cm2; Hanboonsong et al., 2013). Given farmers’ reports of cricket attempted escape, aggression and cannibalism, it seems that whatever stocking densities actually are, they may frequently exceed the limit for high-welfare conditions.
Barrett, M., et al. “Welfare Considerations for Farming Black Soldier Flies, Hermetia Illucens (Diptera: Stratiomyidae): A Model for the Insects as Food and Feed Industry.” Journal of Insects as Food and Feed, vol. 9, no. 2, Aug. 2022, pp. 119–148, https://doi.org/10.3920/jiff2022.0041.
Barrett, M., et al. “Farmed Yellow Mealworm (Tenebrio Molitor; Coleoptera: Tenebrionidae) Welfare: Species-Specific Recommendations for a Global Industry.” Journal of Insects as Food and Feed, vol. 10, no. 6, 15 Dec. 2023, pp. 903–948, https://doi.org/10.1163/23524588-20230104.
Rowe, E, et al. “Farmed Cricket (Acheta Domesticus, Gryllus Assimilis, and Gryllodes Sigillatus; Orthoptera) Welfare Considerations: Recommendations for Improving Global Practice.” Journal of Insects as Food and Feed, vol. 10, no. 8, 5 Mar. 2024, pp. 1253–1311, https://doi.org/10.1163/23524588-00001087.
^
Barrett et al., 2022, writes:
Disease outbreaks are common in many farmed invertebrate populations and can result in significant mortality, as well as symptom-related suffering and loss of natural behaviours before death. Apparent symptoms of insect diseases vary based on the pathogen, but may be associated with suffering prior to potential mortality, including behavioural changes, lethargy, sepsis, swollen abdomens, feeding cessation, and more (Joosten et al., 2020).
BSF may be less likely to experience large-scale disease outbreaks compared to other farmed insect species. Not a single large-scale disease outbreak had been reported by 20 international BSF producers as of 2015 (Eilenberg et al., 2015), and the larvae may be more resistant to pathogens due to their specially adapted immune system (Joosten et al., 2020; Zdybicka-Barabas et al., 2017). . However, anecdotal accounts by BSF producers suggest pathogens are a more serious concern than currently reported in the literature: ‘there are unpreferable fungi that could hurt the colony… and some attacks will result in population wipeout… A virus infection usually kills over 90% of the larvae’ (Yang, 2017a) and ‘there is a good chance you will experience a disease outbreak. Some may even say it is inevitable… [you will] understand the frustration in losing some or all of your colony’ (Miranda, 2021)
…In addition to diseases, other parasitic organisms may impact farmed BSF welfare, including mites (Acari), phorids (Diptera: Phoridae), nematodes (Nematoda), and wasps
(Hymenoptera), which all impact other Diptera (Khoobdel et al., 2019; Müller et al., 2017; Perez-Leanos et al., 2017).
On mealworms, Barrett et al., 2023, continues:
YM are host to a number of endoparasites including viruses, bacteria, protists, microsporidia, and fungi… Virulence can range from nearly undetectable to rapid symptom onset and death (Table 2). Both the severity and duration of welfare impacts, prior to death, will be relevant to the insect’s welfare. Endoparasites may influence an insect’s welfare by restricting their behavior (e.g. movement, feeding, or memory deficits), inducing malnourishment, damaging or distending the body (Eilenberg et al., 2018), or even causing mortality. These changes may result in a variety of negative affective states, such as hunger in response to malnourishment or pain in response to prolonged mortality.
On crickets, Rowe et al., 2024, notes:
Crickets’ interactions with microorganisms can often be detrimental; though not always lethal, many sublethal symptoms may still represent a threat to both the individual’s welfare and economic productivity.
…AdDNV is the most well-known disease affecting farmed crickets, resulting in millions of dollars of losses due to multiple large-scale outbreaks in Europe and North America over 35 years (Styer and Hamm, 1991; Szelei et al., 2011). AdDNV spreads via fecal-oral transmission or cannibalism (Weissman et al., 2012) and can lead to high mortality (up to 100%) of farmed crickets (Liu et al., 2011; Szelei et al., 2011)… The virus affects the last three nymphal instars and/or the emerging adult. Infected adult females lived a maximum of 14 days, compared to 30-40 days for uninfected females (Liu et al., 2011; Szelei et al., 2011). The disease paralyzes crickets prior to death: the digestive tract does not contract, and they may lay on their backs, paralyzed, for several days before finally dying, reportedly of septicemia (Maciel-Vergara et al., 2021; Maciel-Vergara and Ros, 2017). Individuals can be observed with a swollen abdomen and liquified inner tissue (Maciel-Vergara et al., 2021). Death is slow (Szelei et al., 2011) and therefore of significant welfare concern.
…Beyond disease agents, crickets may also be affected by a variety of nematoidan (nematoda or nematomorpha) parasites. Entomopathogenic nematodes are microscopic, wormlike animals that parasitize insects, generally with a broad host range. As necrotrophic parasites, there is a high likelihood of mortality for infected insects (Agrios, 2009).
Barrett, M., et al. “Welfare Considerations for Farming Black Soldier Flies, Hermetia Illucens (Diptera: Stratiomyidae): A Model for the Insects as Food and Feed Industry.” Journal of Insects as Food and Feed, vol. 9, no. 2, Aug. 2022, pp. 119–148, https://doi.org/10.3920/jiff2022.0041.
Barrett, M., et al. “Farmed Yellow Mealworm (Tenebrio Molitor; Coleoptera: Tenebrionidae) Welfare: Species-Specific Recommendations for a Global Industry.” Journal of Insects as Food and Feed, vol. 10, no. 6, 15 Dec. 2023, pp. 903–948, https://doi.org/10.1163/23524588-20230104.
Rowe, E, et al. “Farmed Cricket (Acheta Domesticus, Gryllus Assimilis, and Gryllodes Sigillatus; Orthoptera) Welfare Considerations: Recommendations for Improving Global Practice.” Journal of Insects as Food and Feed, vol. 10, no. 8, 5 Mar. 2024, pp. 1253–1311, https://doi.org/10.1163/23524588-00001087.
^
On black soldier flies, Barrett et al., 2022, notes:
BSF larval cannibalism may also be more common than anecdotally reported. Larval cannibalism of emerging adults has been recorded (Furman et al., 1959), as well as consumption of dead and live larvae/pupae, particularly when reared in high density… Cannibalism of adults by larvae seems common (reviewed in Nguyen, 2010; Barrett, pers. comm.).
On mealworms, Barrett et al., 2023, writes:
For YML, high stocking densities can contribute to cannibalism – particularly of smaller larvae or pupae (which are particularly vulnerable due to their relative immobility; Ichikawa and Kurauchi, 2009). Cannibalism may not result in the immediate death of the cannibalized individual; instead, they may simply be injured but remain alive for hours (or days; Ichikawa and Kurauchi, 2009) prior to succumbing to hemolymph loss or putative septicemia (Weaver and McFarlane, 1990). Non-lethal wounds caused by cannibalism breach the cuticle, with holes that may be several mm in diameter (Weaver and McFarlane, 1990), and thus may also increase instances of disease (see Concern 5). High larval rearing density may increase cannibalism, especially at later larval stages (Weaver and McFarlane, 1990; but see Zaelor and Kitthawee, 2018 where no effect was found). As density increased from 2 to 20 individuals/455 ml rearing jar, survival to pupation declined from 94% to 47.5%. Cannibalism was only observed at the higher densities (Weaver and McFarlane, 1990)
Finally, on crickets, Rowe et al., 2024, writes:
Alongside aggression, cannibalism is reported as a frequent behavior in many cricket species (Nakajima and Ogura, 2022), though both cannibalism and aggression are reported as rare in G. sigillatus, specifically, on farms (Mazurkiewicz et al., 2013). Cricket producers (species not specified) in the UK have reported cannibalism as an issue on their farms (Bear, 2019), and some have observed larger A. domesticus cannibalize smaller conspecifics (Crocker and Hunter, 2018). However, it is presently unclear whether cannibalism is a cause of mortality, or simply a consequence of mortality caused by other factors, in A. domesticus and G. assimilis.
Barrett, M., et al. “Welfare Considerations for Farming Black Soldier Flies, Hermetia Illucens (Diptera: Stratiomyidae): A Model for the Insects as Food and Feed Industry.” Journal of Insects as Food and Feed, vol. 9, no. 2, Aug. 2022, pp. 119–148, https://doi.org/10.3920/jiff2022.0041.
Barrett, M., et al. “Farmed Yellow Mealworm (Tenebrio Molitor; Coleoptera: Tenebrionidae) Welfare: Species-Specific Recommendations for a Global Industry.” Journal of Insects as Food and Feed, vol. 10, no. 6, 15 Dec. 2023, pp. 903–948, https://doi.org/10.1163/23524588-20230104.
Rowe, E, et al. “Farmed Cricket (Acheta Domesticus, Gryllus Assimilis, and Gryllodes Sigillatus; Orthoptera) Welfare Considerations: Recommendations for Improving Global Practice.” Journal of Insects as Food and Feed, vol. 10, no. 8, 5 Mar. 2024, pp. 1253–1311, https://doi.org/10.1163/23524588-00001087.
^
Injury in black soldier flies: (Barrett et al., 2022):
BSF larval bodies are soft, making them susceptible to injuries caused by sharp objects. Injury may not kill a larva, but can dramatically increase infection risks – injured BSF are more susceptible to entomopathogenic nematode infection (with increased mortality resulting from infection; Tourtois et al. (2017)) and injured larvae have increased immune system activity following challenge with nonsterile environments (Zdybicka-Barabas et al., 2017). Injury may be caused by improperly prepared substrates containing sharp material, inappropriate handling, or cannibalism.
On mealworms, Barrett et al., 2023, mentions injury only in the context of cannibalism (which we’ve already discussed).
On crickets, Rowe et al., 2024, found:
To date, there are no specific reports on the effects of crowding or aggression on injury rates in A. domesticus, G. assimilis, or G. sigillatus. Injuries to the antennae, cerci, and legs resulting from fighting have been reported anecdotally for some cricket species (Alexander, 1961; Sandford, 1987; Simmons, 1986), and incidence of bodily injury (especially damage to antennae) has been shown to increase with rearing density for the cricket Velarifictorus micado in laboratory colonies, most likely through fighting (although this species is particularly aggressive and may not be representative of the focal species’ behaviors; Wu et al., 2014).
Barrett, M., et al. “Welfare Considerations for Farming Black Soldier Flies, Hermetia Illucens (Diptera: Stratiomyidae): A Model for the Insects as Food and Feed Industry.” Journal of Insects as Food and Feed, vol. 9, no. 2, Aug. 2022, pp. 119–148, https://doi.org/10.3920/jiff2022.0041.
Barrett, M., et al. “Farmed Yellow Mealworm (Tenebrio Molitor; Coleoptera: Tenebrionidae) Welfare: Species-Specific Recommendations for a Global Industry.” Journal of Insects as Food and Feed, vol. 10, no. 6, 15 Dec. 2023, pp. 903–948, https://doi.org/10.1163/23524588-20230104.
Rowe, E, et al. “Farmed Cricket (Acheta Domesticus, Gryllus Assimilis, and Gryllodes Sigillatus; Orthoptera) Welfare Considerations: Recommendations for Improving Global Practice.” Journal of Insects as Food and Feed, vol. 10, no. 8, 5 Mar. 2024, pp. 1253–1311, https://doi.org/10.1163/23524588-00001087.
^
Handling stress in black soldier flies (Barrett et al., 2022):
Larvae are subjected to handling and disturbance, which may cause injury or stress (particularly if photophobic larvae are exposed to light)… More research is needed about how/if disturbance stresses BSF larvae but, given that most organisms react negatively to handling, it is safe to assume that handling may cause larvae some degree of discomfort (Baumann, 2019).
…BSF adults are also likely to be stressed by handling or human activity: interruptions (apparently caused by movement or noise) can even cause mating to cease, and producers recommend keeping BSF adults in out-of-theway locations to avoid disturbance (Yang, 2017a).
Handling stress in mealworms (Barrett et al., 2023):
Light may be necessary during rearing or processing so that facility staff can safely complete their work. However, YM adults are nocturnal and photophobic (Balfour and Carmichael, 1928; Cloudsley-Thompson, 1953; Sheiman and Kreschenko, 2010). Larvae also demonstrate a strong preference for darkness (Howard, 1955; Loeb, 1905); YML bury themselves in the feeding substrate when exposed to light and will move away from introduced light even when no substrate is provided (Balfour and Carmichael, 1928; Howard, 1955). In fact, both larvae and adults avoid light more strongly than the lethal insect repellant, paradichlorobenzene (Howard, 1955).
…Handling events may be superficially similar to predator threats, such as being physically handled or the feeling of vibrations in the substrate; for this reason, handling may cause stress or possibly even fear-like states for insects. Predators are linked ttress hormone release in many insects (Cinel et al., 2020), resulting in a suite of evolved anti-predator behavioral responses, such as tonic immobility (Humphreys and Ruxton, 2018)… Increased stress in response to handling has not been studied in YML, though ‘violent locomotion’ is reported in response to rough handling (see discussion in Cloudsley-Thompson, 1953).
…Pre-slaughter handling may prove to be a particularly stressful experience for YML, as vibrating sieves may be used to separate YML from the feed. It’s unclear if the vibrations produced by machinery are experienced similarly to the vibrations produced by predators that can cause stress in insects.
Handling stress in crickets (Rowe et al., 2024):
In A. domesticus, handling induced a hyperglycaemic and hyperlipaemic response (an increase of sugar and lipids in the plasma to mobilize energy resources). Levels of the neurotransmitter octopamine increased rapidly in response to handling and decreased rapidly when the stressor was removed (Woodring et al., 1988, 1989). Octopamine is called the insect “fight or flight” hormone (Orchard, 1982; Roeder, 1999) or stress hormone (Adamo and Baker, 2011). Although there are no data on handling-associated stress in G. assimilis and G. sigillatus, the widespread association between handling and octopamine release in insects (Bailey et al., 1984; Harris and Woodring, 1992; Orchard et al., 1981) would suggest that they may also experience stress when handled.
Other disturbances can also induce stress: for instance, overhead shadows (e.g. of humans or equipment) can be perceived as a predation threat (as in Drosophila fruit flies; Gibson et al., 2015), as can vibrations (see concern 13). As crickets are intensely photophobic, and exhibit negative phototaxis, light may also induce stress; however, light is routinely used in harvesting or maintenance.
Barrett, M., et al. “Welfare Considerations for Farming Black Soldier Flies, Hermetia Illucens (Diptera: Stratiomyidae): A Model for the Insects as Food and Feed Industry.” Journal of Insects as Food and Feed, vol. 9, no. 2, Aug. 2022, pp. 119–148, https://doi.org/10.3920/jiff2022.0041.
Barrett, M., et al. “Farmed Yellow Mealworm (Tenebrio Molitor; Coleoptera: Tenebrionidae) Welfare: Species-Specific Recommendations for a Global Industry.” Journal of Insects as Food and Feed, vol. 10, no. 6, 15 Dec. 2023, pp. 903–948, https://doi.org/10.1163/23524588-20230104.
Rowe, E, et al. “Farmed Cricket (Acheta Domesticus, Gryllus Assimilis, and Gryllodes Sigillatus; Orthoptera) Welfare Considerations: Recommendations for Improving Global Practice.” Journal of Insects as Food and Feed, vol. 10, no. 8, 5 Mar. 2024, pp. 1253–1311, https://doi.org/10.1163/23524588-00001087.
^
Starvation in black soldier flies (Barrett et al., 2022):
Adult BSF are generally kept without food due to a widely held belief that they may live entirely off of energy reserves built during the larval stage (Caruso et al., 2013; Sheppard et al., 2002; Yang, 2017a)… These data suggest that the current practices do not provide adult BSF with freedom from hunger, resulting in premature mortality due to starvation and representing significant potential for suffering.
…Some producers starve, or ‘fast’, insects prior to slaughter for 1-2 days in order to empty the insects’ guts (Van Huis, 2021), though how common this feed withdrawal practice is in the BSF industry is unclear (Larouche, 2019).
Starvation in mealworms (Barrett et al., 2023):
Fasting, a period of starvation for 1-2 days prior to slaughter, clears the digestive systems of YML so less frass makes it into the final product (Spranghers et al., 2021; van Huis, 2021).
Starvation in crickets (Rowe et al., 2024):
Cricket producers in the UK report that during periods of starvation prior to harvesting, crickets “start eating each other” if the period is too great (Bear, 2019). A maximum fasting length of 24 hours is thus recommended to reduce cannibalism (and see concern 1).
Barrett, M., et al. “Welfare Considerations for Farming Black Soldier Flies, Hermetia Illucens (Diptera: Stratiomyidae): A Model for the Insects as Food and Feed Industry.” Journal of Insects as Food and Feed, vol. 9, no. 2, Aug. 2022, pp. 119–148, https://doi.org/10.3920/jiff2022.0041.
Barrett, M., et al. “Farmed Yellow Mealworm (Tenebrio Molitor; Coleoptera: Tenebrionidae) Welfare: Species-Specific Recommendations for a Global Industry.” Journal of Insects as Food and Feed, vol. 10, no. 6, 15 Dec. 2023, pp. 903–948, https://doi.org/10.1163/23524588-20230104.
Rowe, E, et al. “Farmed Cricket (Acheta Domesticus, Gryllus Assimilis, and Gryllodes Sigillatus; Orthoptera) Welfare Considerations: Recommendations for Improving Global Practice.” Journal of Insects as Food and Feed, vol. 10, no. 8, 5 Mar. 2024, pp. 1253–1311, https://doi.org/10.1163/23524588-00001087.
^
As far as we can tell, this is primarily an issue for mealworms and crickets.
On mealworms, Barrett et al., 2023, notes:
YML may also be sold live to zoos, pet stores, direct to consumer, etc., for feeding to exotic/pet animals, in which case they must be transported. It is recommended to transport YML refrigerated (Spranghers et al., 2021). However, they may be shipped live directly to consumers in containers without climate control, water, or food… The process of shipping, inappropriate storage practices, and neglect or inexperience by consumers and pet stores can result in starvation, desiccation stress, disease, cannibalism, and more… Vibrations from transport vehicles may induce stress.
On crickets, Rowe et al., 2024, notes:
Crickets may be transported live to markets in small mesh pens, such as in Thailand, for home consumption (Halloran et al., 2016). Crickets may also be transported live for exotic pet feed – in the USA alone, an estimated 2.6 billion live crickets were shipped for this purpose in 2012 (Weissman et al., 2012). Some, though not all, producers may provide feed and moisture sources during transit (Cricket King, n.d.; Josh’s Frogs, n.d.; Suckling et al., 2020).
…Vibrations induce anti-predator behaviors in crickets (Dambach, 1989). Octopamine levels increased in Gryllus texensis crickets subjected to vibrations in their rearing container (Adamo and Baker, 2011). Provisioning cricket rearing environments with hiding places may mitigate these effects – in a subsequent study, crickets exposed to the same mock predator spent more time under a cardboard shelter compared to controls (Adamo et al., 2013). Repeated exposure to the mock vibrating predator increased basal octopamine levels (Adamo and Baker, 2011), similar to the effects of chronic stress on the basal levels of vertebrate stress hormones.
Exposure to vibrations during transportation is likely to be a welfare concern, potentially contributing to high mortality. Producers report that live transport, generally used when shipping crickets as pet feed, frequently causes mortality: “even when packed with care, the physical stress of travel can shorten the overall lifespan of the crickets” (Josh’s Frogs, n.d.; Barrett, pers. comm.). Mazurkiewicz et al. (2013) claim that crickets “are usually weak and soon die of exhaustion [from] conditions of transportation” when imported. This phenomenon may be called ‘shipping sickness’ in the industry and producers may even include extra crickets to cover those expected to die in the delivery process (e.g. 20% extra provided by Cricket King, n.d.). Given that most motorized transportation methods will include significant vibrations, crickets may experience significant stress during transport.
Barrett, M., et al. “Farmed Yellow Mealworm (Tenebrio Molitor; Coleoptera: Tenebrionidae) Welfare: Species-Specific Recommendations for a Global Industry.” Journal of Insects as Food and Feed, vol. 10, no. 6, 15 Dec. 2023, pp. 903–948, https://doi.org/10.1163/23524588-20230104.
Rowe, E, et al. “Farmed Cricket (Acheta Domesticus, Gryllus Assimilis, and Gryllodes Sigillatus; Orthoptera) Welfare Considerations: Recommendations for Improving Global Practice.” Journal of Insects as Food and Feed, vol. 10, no. 8, 5 Mar. 2024, pp. 1253–1311, https://doi.org/10.1163/23524588-00001087.
^
Barrett et al., 2022, notes:
Currently, no data are available on the welfare impacts of different slaughter methods for insects, and no welfare regulations exist to guide farmers in determining humane slaughter standard operating procedures (SOPs, Bear, 2019; Delvendahl et al., 2022).
Slaughter of black soldier flies (Barrett et al., 2022):
Current methods of slaughter for BSF larvae include: freezing (in air or liquid nitrogen), baking in a convection oven, roasting in sand or sunshine, microwaving, boiling/blanching, asphyxiation, and grinding/shredding (EAWAG, n.d.; Larouche et al., 2019; Mat et al., 2021). BSF larvae may be sold prior to slaughter and consumed live by pets or livestock without anaesthetic.
…Boiling/blanching, freezing in liquid nitrogen, and grinding are likely to be the most humane slaughter methods based solely on time-to-death (see also, Hakman et al., 2013)
When sand roasting is used, sand is heated in a pan or rotating drum to >150-200 °C prior to the addition of larvae in a 1:1 or 2:3 larvae-to-sand ratio (EAWAG, n.d.). Conductive heat transfer between larvae and the sand should raise larvae to lethal temperatures very quickly, once fully immersed. However, both rotating drums and pans may not immerse all larvae entirely within the sand instantly, limiting conductive heat transfer to many larvae in the first few seconds of exposure. Convective heat transfer from hot air above the sand surface will heat larvae more slowly
…Microwaving insects will kill them by dielectric heating (described in Yadav et al. (2014)). Microwaving appears to be relatively common for BSF larvae; machines can process more than 4,000 W/kg of fresh larvae (dependent on SOP and microwave power) and are typically 2,450 MHz. The process of completely drying out larvae takes 6-15 minutes (EAWAG, n.d.; MAX Industrial Microwaves, 2016, n.d), but death will occur sooner, as larvae reach CTmax. A 500 W microwave source killed 100% of smaller-bodied red flour beetle (Tribolium castaneum, Coleoptera: Tenebrionidae) larvae within 28 seconds (in a 50 gram sample of grain, so 10,000 W/kg of material; Vadivambal et al., 2008).
Sun baking will take several hours, depending on ambient temperature, relative humidity, and solar intensity, to kill BSF larvae either through desiccation or overheating. In addition, BSF larvae are photophobic (Canary et al., 2009; Newton, n.d.), and will attempt to move away from the sunlight during this method of slaughter, suggesting that sunlight likely induces additional stress (Mat et al., 2021)
…Ovens are typically heated to 60-65 °C (EAWAG, n.d.; Larouche et al., 2019). Both the lower air temperatures in oven baking (as compared to sand roasting or blanching), and slower transfer of heat from the air to the larvae, suggest that this method will not be instantaneous and could take many seconds to a few minutes to kill all larvae, depending on SOP.
…Freezing in air has been considered, anecdotally (Bear, 2019; Erens et al., 2012), a humane method of insect euthanasia because it is thought to anaesthetise the insect prior to death by gradually chilling them. However cold does not have any analgesic effects and is not considered humane as an anaesthetic for invertebrates according to veterinary practitioners (AVMA, 2020; Cooper, 2001; Gunkel and Lewbart, 2007; Pellett et al., 2013). Murray (2012) even recommends the use of an inhalation anaesthetic prior to any freezing-based slaughter methods.
…Insect death by suffocation is generally slow (many hours). The larvae/nymph stages of 12 different insect museum pests took between 3 and 144 hours to achieve 100% mortality (Rust and Kennedy, 1993). Hypoxic conditions induce hyperventilation and loss of spiracular control,significantly increasing water loss and causing desiccation.
…The use of anaesthetics prior to slaughter does not appear to be a standard practice in the BSF industry (but see Bear, 2019).
Slaughter of mealworms (Barrett et al., 2023):
YML are not typically stunned or anesthetized prior to slaughter. The most common slaughter methods include microwaving, drying in a convection oven, air freezing, shredding/grinding, and steam blanching or boiling (Bordiean et al., 2020; Spranghers et al., 2021; van Huis and Tomberlin, 2017). Often freezing, or blanching/boiling, will be used prior to drying (EFSA, 2015; Selaledi and Mabelebele, 2021; Sindermann et al., 2021; Vandeweyer et al., 2017b).
Slaughter of crickets (Rowe et al., 2024):
Reported slaughter methods for crickets include boiling (described as the most common method in Thailand; Reverberi, 2020), immersion in pressurized steam (Tatarova, 2017), immersion in hot, non-boiling water (e.g. 60 °C; Vandeweyer et al., 2018), drowning in non-boiling water (Fernandez-Cassi et al., 2019; Miech, 2018), freezing in air (e.g. 24 hours at −18 °C, Bear, 2019; Fernandez-Cassi et al., 2019), heating (presumably in dry air; Fernandez-Cassi et al., 2019), shredding (Bear, 2019), and asphyxiation (Singh et al., 2020). Freezing in air is reported to be the main slaughter method for mass-produced crickets (van Huis et al., 2013). Anesthetic use is not widely reported before slaughter; however, at least one cricket producer has self-reported using carbon dioxide gas as an anesthetic before freezing (Bear, 2019).
Barrett, M., et al. “Welfare Considerations for Farming Black Soldier Flies, Hermetia Illucens (Diptera: Stratiomyidae): A Model for the Insects as Food and Feed Industry.” Journal of Insects as Food and Feed, vol. 9, no. 2, Aug. 2022, pp. 119–148, https://doi.org/10.3920/jiff2022.0041.
Barrett, M., et al. “Farmed Yellow Mealworm (Tenebrio Molitor; Coleoptera: Tenebrionidae) Welfare: Species-Specific Recommendations for a Global Industry.” Journal of Insects as Food and Feed, vol. 10, no. 6, 15 Dec. 2023, pp. 903–948, https://doi.org/10.1163/23524588-20230104.
Rowe, E, et al. “Farmed Cricket (Acheta Domesticus, Gryllus Assimilis, and Gryllodes Sigillatus; Orthoptera) Welfare Considerations: Recommendations for Improving Global Practice.” Journal of Insects as Food and Feed, vol. 10, no. 8, 5 Mar. 2024, pp. 1253–1311, https://doi.org/10.1163/23524588-00001087.
^
Phrase borrowed from Luke Muehlhauser’s 2017 report on consciousness and moral patienthood.
^
This report was conducted while Muehlhauser was a Research Analyst at Open Philanthropy. Open Philanthropy is 80,000 Hours’ largest funder. We’re referencing this report not because Muehlhauser is an expert in the area (he doesn’t have a background in the subject) or because we agree with its assumptions or conclusions (I don’t — I’m particularly sceptical of assuming functionalism and illusionism), but rather because it’s an unusually broad and transparent review. If you’re interested in reading more about animal consciousness, we’d recommend taking a look at the full report, as well as its extensive list of sources.
^
This seems reasonable because it is a relatively theory-agnostic measure of “similarity to humans.” The data in the table below are rounded median estimates from TimeTree (a public database of published studies into evolutionary timescales).
^
Meuhlheuser notes that play behaviour was proposed as an indicator of consciousness in Rial et al., 2007.
…[P]lay shows several traits indicative of consciousness. Besides of [sic] being an onerous activity, play seems to be always pleasant. The only explanation for the play paradox lies in considering that the expenditure of energy must have a wide variation in hedonic value, from rather unpleasant to extremely pleasurable, that is, it shows a wide range of alliesthesia. An animal confronted with the possibility of playing should rank the costs and the benefits of each alternative and its final decision will aim at maximizing pleasure. Therefore, the presence of play should be a sign of consciousness.
Rial, R. V. et al. “The Evolution of Consciousness in Animals.” Consciousness Transitions: Phylogenetic, Ontogenetic, and Physiological Aspects, Elsevier, 2007, pp. 45–76.
^
Many theories of consciousness require complex neural behaviour, and this likely correlates with complex cognitive ability.
If you are interested in investigating this in more detail, Muehlhauser’s table of potentially consciousness-indicating features includes a very long list of cognitive abilities that have been linked to consciousness, as well as sources for those claims.
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This is because, even though there are theories where consciousness itself isn’t necessary for moral consideration, most moral theories think that pain is morally relevant.
^
Hartmann, P., et al. “[Normal Weight of the Brain in Adults in Relation to Age, Sex, Body Height and Weight].” Der Pathologe, vol. 15, no. 3, 1 June 1994, pp. 165–170, www.ncbi.nlm.nih.gov/pubmed/8072950, https://doi.org/10.1007/s002920050040.
Based on more than 8000 autopsies of male and female patients without brain diseases the normal brain weight of adult males and females in relation to sex, age, body-weight, and body-height as well as Body Mass Index were calculated. The average brain weight of the adult male was 1336 gr; for the adult female 1198 g
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The most recent study we could find suggests approximately 85 billion, although a wide range of other estimates can be found (approximately 75 to 125 billion).
Azevedo, Frederico A.C., et al. “Equal Numbers of Neuronal and Nonneuronal Cells Make the Human Brain an Isometrically Scaled-up Primate Brain.” The Journal of Comparative Neurology, vol. 513, no. 5, 10 Apr. 2009, pp. 532–541, https://doi.org/10.1002/cne.21974.
We find that the adult male human brain contains on average 86.1 ± 8.1 billion NeuN-positive cells (“neurons”) and 84.6 ± 9.8 billion NeuN-negative (“nonneuronal”) cells.
Lent, Roberto, et al. “How Many Neurons Do You Have? Some Dogmas of Quantitative Neuroscience under Revision.” European Journal of Neuroscience, vol. 35, no. 1, 13 Dec. 2011, pp. 1–9, https://doi.org/10.1111/j.1460-9568.2011.07923.x.
Data provided by different authors have led to a broad range of 75–125 billion neurons in the whole brain.
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The mean brain weight of the 80 chickens evaluated in Rehkämper et al. (2003) was 3.5g with a standard deviation of 0.7g.
These chickens were males and females from the following breeds: Japanese Bantam, Pekin Bantam, Silky chicken, White Crested Polish chicken, Arucana, Breda, Red Leghorn (Italiener), Malayan. It’s unclear the extent to which these are representative of the chickens on factory farms that are bred for growing rate or egg-laying rate, such as the Cobb500 or the Bovans Brown.
Rehkämper, Gerd, et al. “Discontinuous Variability of Brain Composition among Domestic Chicken Breeds.” Brain, Behavior and Evolution, vol. 61, no. 2, 2003, pp. 59–69, https://doi.org/10.1159/000069352.
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Olkowicz et al., 2016, surveyed three red junglefowl and estimated a mean 220.84 million total brain neurons, with a standard deviation of 44.50 (see table S1). Red junglefowl (Gallus gallus) is the non-domesticated ancestor of the chicken. Chickens (Gallus gallus domesticus) are considered a subspecies of red junglefowl. It’s unclear the extent to which red junglefowl are representative of the chickens on factory farms.
Olkowicz, Seweryn, et al. “Birds Have Primate-like Numbers of Neurons in the Forebrain.” Proceedings of the National Academy of Sciences, vol. 113, no. 26, 13 June 2016, pp. 7255–7260, https://doi.org/10.1073/pnas.1517131113.
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By most definitions, “the neocortex… appears only in mammals.” (Lourenço et al., 2020)
However, there is some terminological debate about whether any non-mammals should be considered to have a neocortex.
According to Reiner et al., 2004:
The standard nomenclature that has been used for many telencephalic and related brainstem structures in birds is based on flawed assumptions of homology to mammals. In particular, the outdated terminology implies that most of the avian telencephalon is a hypertrophied basal ganglia, when it is now clear that most of the avian telencephalon is neurochemically, hodologically, and functionally comparable to the mammalian neocortex, claustrum, and pallial amygdala (all of which derive from the pallial sector of the developing telencephalon).
Similarly, according to Jarvis et al., 2005:
Our current understanding of the avian brain — in particular the neocortex-like cognitive functions of the avian pallium — requires a new terminology that better reflects these functions and the homologies between avian and mammalian brains.
And in Stetka, 2020:
For years it was assumed that the avian brain was limited in function because it lacked a neocortex… The new findings show that birds’ do, in fact, have a brain structure that is comparable to the neocortex despite taking a different shape. It turns out that at a cellular level, the brain region is laid out much like the mammal cortex, explaining why many birds exhibit advanced behaviors and abilities that have long befuddled scientists.
…The mammalian cortex is organized into six layers containing vertical columns of neurons that communicate with one another both horizontally and vertically. The avian brain, on the other hand, was thought to be arranged into discrete collections of neurons called nuclei, including a region called the dorsal ventricular ridge, or DVR, and a single nucleus named the wulst.
…”It’s not that the DVR is the neocortex,” says Vanderbilt University neuroscientist Suzana Herculano-Houzel, who wrote a commentary accompanying the two new papers and was not involved in either of them, “but rather that the whole of the pallium in mammals and in birds has similar developmental origins and connectivity, and therefore [the pallia of both classes] should be considered equivalent structures. Stacho shows that settling for what the naked eye sees can be misleading.”
Chickens have a dorsal ventricular ridge in their pallium (Ahumada-Gelleguillois, 2015).
Lourenço, Joana, et al. “Synaptic Inhibition in the Neocortex: Orchestration and Computation through Canonical Circuits and Variations on the Theme.” Cortex, vol. 132, 1 Nov. 2020, pp. 258–280, https://doi.org/10.1016/j.cortex.2020.08.015.
Reiner, Anton, et al. “Revised Nomenclature for Avian Telencephalon and Some Related Brainstem Nuclei.” The Journal of Comparative Neurology, vol. 473, no. 3, 31 May 2004, pp. 377–414, https://doi.org/10.1002/cne.20118.
Jarvis, Erich D., et al. “Avian Brains and a New Understanding of Vertebrate Brain Evolution.” Nature Reviews Neuroscience, vol. 6, no. 2, Feb. 2005, pp. 151–159, https://doi.org/10.1038/nrn1606.
Stetka, Bret. “Bird Brains Are Far More Humanlike than Once Thought.” Scientific American, 24 Sept. 2020, www.scientificamerican.com/article/bird-brains-are-far-more-humanlike-than-once-thought/.
Ahumada-Galleguillos, Patricio, et al. “Anatomical Organization of the Visual Dorsal Ventricular Ridge in the Chick (Gallus Gallus): Layers and Columns in the Avian Pallium.” The Journal of Comparative Neurology, vol. 523, no. 17, 1 Dec. 2015, pp. 2618–2636, pubmed.ncbi.nlm.nih.gov/25982840/, https://doi.org/10.1002/cne.23808.
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Minervini et al., 2016, measured the mass of the brains of 26 adult pigs (Sus scrofa domesticus), 8 Large Whites and 18 cross-breed Danish Landrace and Large White.
According to Miervini et al., 2016:
Pure or cross-bred LR [Landrace] pigs include more than 90% of all pigs commercially raised in the Western world. The LW [Large White] breed is the other popular breed used in animal production all over the world.
They found an average adult brain massof 134.5g (table 3), with a standard error of the mean of 2.45g (equivalent to a standard deviation of 12.5g).
Minervini, Serena, et al. “Brain Mass and Encephalization Quotients in the Domestic Industrial Pig (Sus Scrofa).” PLOS ONE, vol. 11, no. 6, 28 June 2016, p. e0157378, https://doi.org/10.1371/journal.pone.0157378.
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This is the number of neurons in the brain of domestic pigs, the most common breed of pig commercially raised in the Western world, according to Jelsing et al., 2006 (table 1). Specifically, Jelsing et al., 2006, studied crossbreeds between Danish Landrace and Yorkshire.
There’s substantial variation in this number: neonatal pigs had 260 million neurons. The Göttingen minipig, the smallest breed of domestic pig, had 250 million neurons (neonate) and 290 million (adult).
Jelsing, Jacob, et al. “The Postnatal Development of Neocortical Neurons and Glial Cells in the Göttingen Minipig and the Domestic Pig Brain.” The Journal of Experimental Biology, vol. 209, no. 8, 15 Apr. 2006, pp. 1454–1462, https://doi.org/10.1242/jeb.02141.
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All mammals have a neocortex. Pigs are mammals. Therefore, pigs have a neocortex.
“The Origin and Evolution of Neocortex: From Early Mammals to Modern Humans.” Progress in Brain Research, vol. 250, 1 Jan. 2019, pp. 61–81, https://doi.org/10.1016/bs.pbr.2019.03.017.
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According to Sangiao-Alvarellos et al., 2004, a sample of rainbow trout (Oncorhynchus mykiss) had an average brain mass of 0.238 g.
Khat et al., 2022, looked at brains of common carp (Cyprinus carpio) and found:
The mean value of total weight of hatchery fishes 345±48.68 and the mean value of brain weight of hatchery reared fishes 0.28±0.047. The mean value of wild fish’s total body weight 195.16±52.58 and the mean value of brain weight of wild fishes are 0.45±0.14.
Wiper et al., 2014, found an adult male Chinook salmon (Oncorhynchus tshawytscha) brain was around 1.21 ± 0.027 g in the wild, and more like 1.03 ± 0.019 g in a hatchery.
S. Sangiao‐Alvarellos, et al. “Effects of Central Administration of Arginine Vasotocin on Monoaminergic Neurotransmitters and Energy Metabolism of Rainbow Trout Brain.” Journal of Fish Biology, vol. 64, no. 5, 27 Apr. 2004, pp. 1313–1329, https://doi.org/10.1111/j.0022-1112.2004.00394.x.
Khan, W, et al. “Comparative Analysis of Brain in Relation to the bBdy Length and Weight of Common Carp (Cyprinus Carpio) in Captive (Hatchery) and Wild (River System) populations.” Brazilian Journal of Biology, vol. 82, 2022, p. 242897, [https://doi.org/10.1590/1519-6984.242897](https://doi.org/10.1590/1519-6984.242897.
Wiper, Mallory L., et al. “Early Experience and Reproductive Morph Both Affect Brain Morphology in Adult Male Chinook Salmon (Oncorhynchus Tshawytscha).” Canadian Journal of Fisheries and Aquatic Sciences, vol. 71, no. 9, Sept. 2014, pp. 1430–1436, https://doi.org/10.1139/cjfas-2013-0624.
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According to Hinsch et al., 2007, who studied zebrafish (Danio rerio):
Zebrafish, like other teleosts, are distinguished by their enormous potential to produce new neurons in many parts of the adult brain. By labeling S-phase cells with the thymidine analog 5-bromo-2′-deoxyuridine (BrdU), quantitative analysis demonstrated that, on average, 6000 new cells were generated in the entire adult brain within any 30 min period. This corresponds to roughly 0.06% of the total number of brain cells.
Doing the calculation, 6000 divided by 0.06% gives 10 million neurons. According to Bone, 2019, most species of fish are teleosts:
The curious relict freshwater species of ancient lines are zoologically interesting, and sturgeons are economically important, but they are completely overshadowed by the dominant bony teleosts and the cartilaginous elasmobranchs of both fresh and salt waters. In numbers of species, teleosts (96% of all living fish) far outweigh the 800 or so elasmobranchs, and have diversified into all kinds of habitat, but elasmobranchs are by no means unsuccessful in other respects and apart from killer whales (Orca), large sharks are the top marine predators, as well as having relatively larger brains than almost all teleosts; and the plankton feeding whale sharks and basking sharks are the largest of all fish.
But we’d guess neuron count varies widely even among teleosts.
Bone, Quentin. “Fish: General Review.” Encyclopedia of Ocean Sciences, 2019, pp. 129–137, https://doi.org/10.1016/b978-0-12-409548-9.10779-1.
Hinsch, K., and G.K.H. Zupanc. “Generation and Long-Term Persistence of New Neurons in the Adult Zebrafish Brain: A Quantitative Analysis.” Neuroscience, vol. 146, no. 2, May 2007, pp. 679–696, https://doi.org/10.1016/j.neuroscience.2007.01.071.
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Key, 2014, argues that fish do not feel pain based on a neocortex-required view of consciousness:
The pallium of fish is non-laminated. It is partitioned into five broad nuclear regions (dorsomedial, dorsolateral, dorsodorsal, dorsoposterior and ventral; Northcutt 2011). While the dorsodorsal pallium is believed to be homologous to the neocortex there remains some controversy as to the definitive homology between these structures (Echleter and Saidel 1981; Northcutt 2008; Braford 2009; Northcutt 2011). There is converging evidence from electrophysiological recordings (Precht et al. 1998; Saidel et al. 2001; Northcutt et al. 2004) and neuroanatomical tracing (Yamamoto and Ito 2008) that, unlike in the neocortex, sensory information such as visual input, is diffusely processed across the fish dorsal pallium, and certainly not localised to multiple interconnected areas that are topographically mapped (Giassi et al. 2012). Evidence is also lacking for canonical microcircuitry subserving fine scale processing of sensory information in the dorsal pallium. This lack of contrast in signal processing does not support the ability of the fish pallium to differentiate sensory modalities with sufficient resolution to allow the emergence of distinct feelings for different sensory modalities.
Overall, we think that neocortex-required views are not clearly correct. See “Is a cortex required for consciousness?” in Muehlhauser’s report for more.
Key, Brian. “Fish Do Not Feel Pain and Its Implications for Understanding Phenomenal Consciousness.” Biology & Philosophy, vol. 30, no. 2, 16 Dec. 2014, pp. 149–165, https://doi.org/10.1007/s10539-014-9469-4.
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Bee brains were studied by Sayol et al., 2020. They studied 93 species of insect in the superfamily Apoidea, whose brain weights can be found in supplementary data 1.
These species had an average brain weight of 1.6mg with a standard deviation of 1.3mg.
Looking only at bees (species in the family Apidae), the average brain mass across the 23 species studied was 3.0mg with a standard deviation of 1.6mg.
Barrett et al., 2022, examined black soldier fly brains (Hermetia illucens). Flies studied had brain masses of 0.4 to 0.7 mg, with a median of 0.6mg.
Snell-Rood et al., 2020, examined 42 species of butterflies and found brain masses ranging from 0.4 to 0.06mg (see figure 4).
Sayol, Ferran, et al. “Feeding Specialization and Longer Generation Time Are Associated with Relatively Larger Brains in Bees.” Proceedings of the Royal Society B: Biological Sciences, vol. 287, no. 1935, 16 Sept. 2020, p. 20200762, https://doi.org/10.1098/rspb.2020.0762.
Barrett, Meghan, et al. “Impacts of Development and Adult Sex on Brain Cell Numbers in the Black Soldier Fly, Hermetia Illucens L. (Diptera: Stratiomyidae).” Arthropod Structure & Development, vol. 70, Sept. 2022, p. 101174, https://doi.org/10.1016/j.asd.2022.101174.
Snell‐Rood, Emilie C., et al. “Nutritional Constraints on Brain Evolution: Sodium and Nitrogen Limit Brain Size.” Evolution, vol. 74, no. 10, 15 Aug. 2020, pp. 2304–2319, https://doi.org/10.1111/evo.14072.
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Keating et al., 2021, examined 32 species of Hymenoptera to count the number of neurons. They found a mean neuron count for the western honey bee (Apis mellifera) of 613,000, with a standard deviation of 128,000. The full dataset analysing other species can be found here.
Barrett et al., 2022, specifically examined the black soldier fly because of its widespread industry use. They found:
Males had 321,776 ± 44,636 cells in their optic lobes compared to 257,566 ± 60,579 for females. Adults had 42,462 ± 5,222 cells in the central brain region.
According to Alivisatos et al., 2013:
For midterm goals (10 years), one could image the entire Drosophila brain (135,000 neurons), the CNS of the zebra-fish (~1 million neurons), or an entire mouse retina or hippocampus, all under a million neurons.
(Drosophila here refers to Drosophila melanogaster, the fruit fly.)
Godfrey, R. Keating, et al. “Allometric Analysis of Brain Cell Number in Hymenoptera Suggests Ant Brains Diverge from General Trends.” Proceedings of the Royal Society B: Biological Sciences, vol. 288, no. 1947, 24 Mar. 2021, https://doi.org/10.1098/rspb.2021.0199.
Barrett, Meghan, et al. “Impacts of Development and Adult Sex on Brain Cell Numbers in the Black Soldier Fly, Hermetia Illucens L. (Diptera: Stratiomyidae).” Arthropod Structure & Development, vol. 70, Sept. 2022, p. 101174, https://doi.org/10.1016/j.asd.2022.101174.
“The Brain Activity Map Project and the Challenge of Functional Connectomics.” Neuron, vol. 74, no. 6, 21 June 2012, pp. 970–974, www.sciencedirect.com/science/article/pii/S0896627312005181, https://doi.org/10.1016/j.neuron.2012.06.006.
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The features here have been chosen because they seem intuitively illustrative to me.
Since we know so little about the exact causes of consciousness, a better approach would be to include almost every proposed potentially consciousness-indicating feature, but that wouldn’t make for an easy-to-read table.
More comprehensive lists can be found in Meuhlhauser’s report and the “Proxy references” sheet of this spreadsheet put together by Rethink Priorities.
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It’s widely accepted that birds have neural nociceptors.
From transduction to transmission, modulation, projection, and perception, birds possess the neurologic components necessary to respond to painful stimuli.
Douglas, Jamie M., et al. “Pain in Birds.” Veterinary Clinics of North America: Exotic Animal Practice, vol. 21, no. 1, Jan. 2018, pp. 17–31, https://doi.org/10.1016/j.cvex.2017.08.008.
Electrophysiological responses of nociceptive sensory afferent fibres in the skeletal muscle of the chicken (Gallus domesticus) were examined using mechanical and chemical stimulation. The activity of single nociceptive afferent fibres was recorded from micro-dissected filaments of the fibular and lateral tibial nerves, which innervate the fibularis longus and lateral gastrocnemius muscles.
Sandercock, Dale A. “Putative Nociceptor Responses to Mechanical and Chemical Stimulation in Skeletal Muscles of the Chicken Leg.” Brain Research Reviews, vol. 46, no. 2, Oct. 2004, pp. 155–162, https://doi.org/10.1016/j.brainresrev.2004.07.020.
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Birds also exhibit withdrawal responses to a variety of noxious treatments that are used as standard in mammalian pain studies, for example foot withdrawal in response to high temperature in parrots, Amazona ventralis, kestrels, Falco sparverius, and chickens, Gallus gallus domesticus (Geelen et al., 2013; Hothersall et al., 2011; Roach & Sufka, 2003; Sanchez-Migallon Guzman et al., 2013), instantaneous removal of the foot from hot water in Japanese quail, Coturnix japonica (Evrard & Balthazart, 2002), as well as movement away from mechanical stimuli (Evrard & Balthazart, 2002; Hothersall et al., 2011).
Sneddon, Lynne U., et al. “Defining and Assessing Animal Pain.” Animal Behaviour, vol. 97, Nov. 2014, pp. 201–212, https://doi.org/10.1016/j.anbehav.2014.09.007.
The existence of the pain withdrawal reflex is sufficiently well-accepted that it has been suggested as a measure to evaluate whether poultry is unconscious after stunning on farms.
The ability to assess the level of unconsciousness (insensibility) in poultry is important on farms and in abattoirs, where the effectiveness of stunning and slaughter needs to be ascertained. Moreover, knowledge of the most reliable indicators of insensibility is essential to producers and researchers responsible for maintaining acceptable levels of poultry welfare. A problem with assessing insensibility in poultry is that no single method is appropriate under all circumstances, and some methods are not practical in field situations. Several measures have been recommended and used to evaluate insensibility in poultry, including brain stem reflexes, such as the corneal reflex, and spinal reflexes, such as the pain withdrawal reflex.
Erasmus, M. A., et al. “Measures of Insensibility Used to Determine Effective Stunning and Killing of Poultry.” The Journal of Applied Poultry Research, vol. 19, no. 3, 1 Sept. 2010, pp. 288–298, https://doi.org/10.3382/japr.2009-00103.
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Lame and sound broilers, selected from commercial flocks, were trained to discriminate between different coloured feeds, one of which contained carprofen. The two feeds were then offered simultaneously and the birds were allowed to select their own diet from the two feeds. In an initial study to assess the most appropriate concentration of drug, the plasma concentrations of carprofen were linearly related to the birds’ dietary intake. The walking ability of lame birds was also significantly improved in a dose-dependent manner and lame birds tended to consume more analgesic than sound birds. In a second study, in which only one concentration of analgesic was used, lame birds selected significantly more drugged feed than sound birds, and that as the severity of the lameness increased, lame birds consumed a significantly higher proportion of the drugged feed.
Danbury, T. C., et al. “Self-Selection of the Analgesic Drug Carprofen by Lame Broiler Chickens.” Veterinary Record, vol. 146, no. 11, 11 Mar. 2000, pp. 307–311, https://doi.org/10.1136/vr.146.11.307.
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Protective behaviour (also known as guarding behaviour or nocifensive behaviour) has been observed in chickens with oral lesions, according to Gentle and Hill (1987):
The behaviour of normal birds and birds with ulcerated buccal lesions was described following oral stimulation with Acetylcholine chloride (ACh) and Bradykinin (BK). Both groups of birds showed normal oral behaviour but a number of birds with oral lesions showed a behaviour pattern which had been previously seen in our laboratory following nociceptive stimulation. The birds remained motionless in a crouch-like stance with the head pulled into the body and a significantly reduced number of alert head movements. The onset and duration of this immobility response was compared with reports of pain in humans in the blister-base test using similar concentrations of ACh and BK. It was concluded that nocifensive responses of the chicken fulfil many of the requirements for the definition of pain in animals.
Protective behaviour has been observed following beak trimming. According to Gentle et al., 1991:
The avian beak is a complex sensory organ [10] with an extensive nerve supply and numerous mechanoreceptors, thermoreceptors and nociceptors [7]. Partial amputation of the beak, which is accomplished by a combination of cutting and cautery, is often performed in commercially reared poultry to prevent or control feather pecking and cannibalism…. One behavioural category which was reduced after partial beak amputation was the use of the beak for activities not related to feeding or drinking. There was a significant reduction in preening and especially in environmental pecking [11]. This restriction of the beak to essential activities only has been interpreted as guarding behaviour, which is commonly seen following a painful injury in man and other mammals [3, 13, 21]. In the present experiment the onset of this guarding behaviour is taken as indicating discomfort or pain.
Similar results regarding beak trimming can be found in Gentle et al.,1990, and Duncan et al., 1989.
Gentle, Michael J., and Fiona L. Hill. “Oral Lesions in the Chicken: Behavioural Responses Following Nociceptive Stimulation.” Physiology & Behavior, vol. 40, no. 6, Jan. 1987, pp. 781–783, https://doi.org/10.1016/0031-9384(87)90283-6.
Gentle, Michael J., et al. “The Onset of Pain Related Behaviours Following Partial Beak Amputation in the Chicken.” Neuroscience Letters, vol. 128, no. 1, July 1991, pp. 113–116, https://doi.org/10.1016/0304-3940(91)90772-l.
Gentle, Michael J., et al. “Behavioural Evidence for Persistent Pain Following Partial Beak Amputation in Chickens.” Applied Animal Behaviour Science, vol. 27, no. 1-2, Aug. 1990, pp. 149–157, https://doi.org/10.1016/0168-1591(90)90014-5.
Duncan, I. J. H., et al. “Behavioural Consequences of Partial Beak Amputation (Beak Trimming) in Poultry.” British Poultry Science, vol. 30, no. 3, Sept. 1989, pp. 479–488, https://doi.org/10.1080/00071668908417172.
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See, for example, Wetland et al., 2021, which classifies the different types of neural nociceptors without a myelin sheath in pig skin.
Werland, Fiona, et al. “Maximum Axonal Following Frequency Separates Classes of Cutaneous Unmyelinated Nociceptors in the Pig.” Journal of Physiology, vol. 599, no. 5, 15 Jan. 2021, pp. 1595–1610, https://doi.org/10.1113/jp280269.
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A withdrawal reflex in response to pain is commonly observed in pigs and multiple studies have investigated it, such as Baars et al., 2016 and Roelofs et al., 2019.
For example, from Roelofs et al., 2019:
Assessment of withdrawal reflex as a sign of spinal nerve function. Assessment of this reflex has previously been described for pigs (
Baars et al., 2013; Nordquist et al., 2017). The withdrawal reflex consists of withdrawal of a limb after application of a noxious stimulus. The coronary band of the claw of each hind limb was pinched using only the examiner’s fingers. Presence or absence of rapid limb withdrawal was scored. In addition, presence or absence of crossed extensor reflex, i.e. extension of the opposite limb, was scored.
Baars, Jan H, et al. “Prediction of Motor Responses to Surgical Stimuli during Bilateral Orchiectomy of Pigs Using Nociceptive Flexion Reflexes and the Bispectral Index Derived from the Electroencephalogram.” Veterinary Journal, vol. 195, no. 3, 1 Mar. 2013, pp. 377–381, https://doi.org/10.1016/j.tvjl.2012.07.011.
Roelofs, Sanne, et al. “Neurological Functioning and Fear Responses in Low and Normal Birth Weight Piglets.” Applied Animal Behaviour Science, vol. 220, Nov. 2019, p. 104853, https://doi.org/10.1016/j.applanim.2019.104853.
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Multiple studies have established this.
Castel et al., 2017, concluded that pigs and humans respond similarly to analgesics:
This study shows that the activity of three analgesics which are commonly used for postoperative analgesia in the clinic, i.e., ropivacaine, bupivacaine and Exparel, exhibited high similarity to humans when tested in a post-incisional model in pigs. The resemblance exhibited in this study includes three major points: the level of activity, the duration of activity and the superiority expected from treatment with Exparel vs. bupivacaine.
Hermansen et al., 1986, analysed multiple analgesics and found buprenorphine works best on pigs.
In conclusion the present results indicate that buprenorphine may be the drug of choice for the prophylactive treatment of postoperative pain in the pig due to its long duration of action and the lack of adverse reactions. Etorphine induces a complete analgesia but of a shorter duration. Further it has a smaller safety margin than buprenorphine. Pethidine only caused a moderate and short lasting analgesia for which reason it does not seem to be suitable for treating postoperative pain in pigs.
Harvey-Clark, et al., 2000, found that:
TTS fentanyl at appropriate doses is a cost effective means of delivering basal analgesia following major surgery in pigs.
Castel, David, et al. “The Effect of Local/Topical Analgesics on Incisional Pain in a Pig Model.” Journal of Pain Research, vol. Volume 10, Sept. 2017, pp. 2169–2175, https://doi.org/10.2147/jpr.s144949.
Hermansen, K., et al. “The Analgesic Effect of Buprenorphine, Etorphine and Pethidine in the Pig: A Randomized Double Blind Cross-over Study.” Acta Pharmacologica et Toxicologica, vol. 59, no. 1, 13 Mar. 2009, pp. 27–35, https://doi.org/10.1111/j.1600-0773.1986.tb00130.x.
Harvey-Clark, C. J., et al. “Transdermal Fentanyl Compared with Parenteral Buprenorphine in Post-Surgical Pain in Swine: A Case Study.” Laboratory Animals, vol. 34, no. 4, 1 Oct. 2000, pp. 386–398, https://doi.org/10.1258/002367700780387750.
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We couldn’t find any academic sources on this, but protective behaviour is described in veterinary sources, for example, in the Merck Veterinary Manual, a widely-used reference manual.
When discussing lameness, the manual notes:
Affected pigs may be visibly limping, unable to rise, or simply less inclined to move to feed and water troughs.
When discussing skin disorders, specifically sarcoptic mange the manual notes:
Affected pigs may attempt to lick the sores or rub them against a sharp or rough surface.
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This is widely accepted among biologists. For example, see Farrell et al., 2011:
Why is fish pain controversial? Fish have a nociceptive system, the simple detection and reflex withdrawal response to noxious stimuli — this is an accepted fact. The debate centers on the idea that fish may experience the suffering or discomfort necessary for pain perception.
The section (“Why is fish pain controversial?”) in Muehlhauser’s report provides a good overview of the broad debate about fish and cortex-required views of consciousness.
Anthony Peter Farrell, et al. Encyclopedia of Fish Physiology: From Genome to Environment. London; Waltham, Ma, Academic Press, An Imprint Of Elsevier, 2011, p.714.
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Chatigny, 2018, provides a comprehensive overview of analgesia in fish.
Some recommendations on the use of analgesics in fish are currently in the literature; however, information on the properties of analgesic drugs in most fish species is still scarce and sometimes misleading. The present review of information on the use of analgesics in fish was thus compiled to help clinicians make an informed decision as to which drug and dose to use. The main agents that have been investigated are opioids, NSAID, and local anesthetics, primarily in rainbow trout and zebrafish. There is presently no overwhelming evidence of efficacy for most analgesics in fish, although beneficial effects on behavior and physiologic parameters have been reported in many instances, especially associated with morphine administration.
Sneddon, 2013, discusses self-administration:
In terms of pain, one of the central pieces of evidence is whether animals will self medicate with painkillers when in pain or are willing to pay a cost to access such pain relief. Many studies in birds and mammals have shown animals will eat food dosed with analgesics upon experiencing painful stimuli. However, fish suspend feeding until they have recovered from a painful event. In order to determine whether fish will pay a cost to accessing pain relief, zebrafish were given access to two chambers, one of which was enriched with gravel, plants and a live shoal behind a transparent barrier. The other chamber was made unfavourable by being barren and brightly lit. Fish selected the enriched chamber to spend most time in and when they had selected the chamber six consecutive times they were assigned to a noxiously stimulated group which had acetic acid injected subcutaneously and a control group with innocuous saline injected. Half of each group were then re- tested and continued to spend most time in the enriched chamber. However, when an analgesic was added to the unfavourable chamber only fish experiencing pain spent time in this chamber shifting their preference. This demonstrates that fish sought analgesia and were willing to pay the cost of being in a brightly, lit barren area where their pain was reduced.
However, Sneddon’s source for this experiment was an unpublished manuscript. Sneddon appears to be somewhat of an advocate for caring about fish, so it’s unclear how to interpret this claim.
Chatigny, Frederic, et al. “Updated Review of Fish Analgesia.” Journal of the American Association for Laboratory Animal Science, vol. 57, no. 1, 2018, pp. 5–12, www.ncbi.nlm.nih.gov/pmc/articles/PMC5875091/.
Sneddon, Lynne U. Do Painful Sensations and Fear Exist in Fish? edited by Thierry Auffret van der Kemp and Martine Lachance, Carswell, 2013, pp. 93–112.
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Rethink Priorities analysed this in detail.
One study of common carp (Cyprinius carpio) shows that when their lips are injected with 5% or 10% acetic acid (as compared to a sham, saline-injected control group of fish), 2 of the 5 study fish exhibited “anomalous” behaviours including rubbing their lips on the tank walls and swimming off balance/losing equilibrium (Reilly et al. 2008). The study also demonstrates that these behaviours decreased in prevalence with time post-injection. Studies of a closely related species, zebrafish (Danio rerio), suggest that injection in the tail with 1% acetic acid causes similarly anomalous behaviours like tail-beating (Maximino 2011). However, Reilly et al. (2008) do not observe anomalous behaviours when zebrafish are injected with 5% or 10% acetic acid in their lips.
To date, there exist no studies of Atlantic or Pacific salmon examining self-protective or “anomalous” behaviours in response to noxious stimuli. However, two studies of very closely related rainbow trout (Oncorhynchus mykiss) indicate that, when their lips are injected with 5% or 10% acetic acid (as compared to a sham, saline-injected control group of fish), they rock side to side on the bottom of the tank and rub their lips in the gravel substrate (Reilly et al. 2008, Sneddon 2003). However, Newby & Stevens (2008) did not observe any of these “anomalous” rocking/rubbing behaviours in a similar study of rainbow trout that attempted to replicate Sneddon (2003)’s findings, and a study from Mettam et al. (2011) expected to see anomalous behaviours in response to acetic acid injection decrease after administration of an analgesic, but report no anomalous behaviours whatsoever.
Reilly, Siobhan C., et al. “Behavioural Analysis of a Nociceptive Event in Fish: Comparisons between Three Species Demonstrate Specific Responses.” Applied Animal Behaviour Science, vol. 114, no. 1-2, Nov. 2008, pp. 248–259, https://doi.org/10.1016/j.applanim.2008.01.016.
Caio Maximino. “Modulation of Nociceptive-like Behavior in Zebrafish (Danio Rerio) by Environmental Stressors.” Psychology & Neuroscience, vol. 4, no. 1, 1 Jan. 2011, pp. 149–155, https://doi.org/10.3922/j.psns.2011.1.017.
Sneddon, Lynne U, et al. “Novel Object Test: Examining Nociception and Fear in the Rainbow Trout.” The Journal of Pain, vol. 4, no. 8, Oct. 2003, pp. 431–440, https://doi.org/10.1067/s1526-5900(03)00717-x.
Newby, Nathalie C, and E. Don Stevens. “The Effects of the Acetic Acid “Pain” Test on Feeding, Swimming, and Respiratory Responses of Rainbow Trout (Oncorhynchus Mykiss).” Applied Animal Behaviour Science, vol. 114, no. 1-2, 1 Nov. 2008, pp. 260–269, https://doi.org/10.1016/j.applanim.2007.12.006.
Mettam, Jessica J., et al. “The Efficacy of Three Types of Analgesic Drugs in Reducing Pain in the Rainbow Trout, Oncorhynchus Mykiss.” Applied Animal Behaviour Science, vol. 133, no. 3-4, Sept. 2011, pp. 265–274, https://doi.org/10.1016/j.applanim.2011.06.009.
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Jang et al., 2023 found that Drosophila respond to painkillers after nociceptive neurons detecting capsaicin (the chemical that makes chillies taste spicy) in their mouths were activated:
In mammals, pain is regulated by the combination of an ascending stimulating and descending inhibitory pain pathway. It remains an intriguing question whether such pain pathways are of ancient origin and conserved in invertebrates. Here we report a new Drosophilapain model and use it to elucidate the pain pathways present in flies. The model employs transgenic flies expressing the human capsaicin receptor TRPV1 in sensory nociceptor neurons, which innervate the whole fly body, including the mouth. Upon capsaicin sipping, the flies abruptly displayed pain-related behaviors such as running away, scurrying around, rubbing vigorously, and pulling at their mouth parts, suggesting that capsaicin stimulated nociceptors in the mouth via activating TRPV1. When reared on capsaicin-containing food, the animals died of starvation, demonstrating the degree of pain experienced. This death rate was reduced by treatment both with NSAIDs and gabapentin, analgesics that inhibit the sensitized ascending pain pathway, and with antidepressants, GABAergic agonists, and morphine, analgesics that strengthen the descending inhibitory pathway. Our results suggest Drosophila to possess intricate pain sensitization and modulation mechanisms similar to mammals, and we propose that this simple, non-invasive feeding assay has utility for high-throughput evaluation and screening of analgesic compounds.
We’d recommend this post to learn more — it summarises the evidence we have about insect pain as presented in Advances in Insect Physiology by Gibbons et al., 2022.
Jang, Wijeong, et al. “Drosophila Pain Sensitization and Modulation Unveiled by a Novel Pain Model and Analgesic Drugs.” PLOS ONE, vol. 18, no. 2, 16 Feb. 2023, p. e0281874, https://doi.org/10.1371/journal.pone.0281874.
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Gibbons et al., 2024, examined the behaviour of bumblebees (Bombus terrestris) after being touched with a hot probe:
It has been widely stated that insects do not show self-protective behavior toward noxiously-stimulated body parts, but this claim has never been empirically tested. Here, we tested whether an insect species displays a type of self-protective behavior: self-grooming a noxiously-stimulated site. We touched bumblebees (Bombus terrestris) on an antenna with a noxiously heated (65°C) probe and found that, in the first 2 min after this stimulus, bees groomed their touched antenna more than their untouched antenna, and more than bees that were touched with an unheated probe or not touched at all did. Our results present evidence that bumblebees display self-protective behavior. We discuss the potential neural mechanisms of this behavior and the implications for whether insects feel pain.
Gibbons, Matilda, et al. “Noxious Stimulation Induces Self-Protective Behavior in Bumblebees.” IScience, 1 July 2024, pp. 110440–110440, https://doi.org/10.1016/j.isci.2024.110440.
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Interestingly, among two-year-old children, only around two-thirds pass this test.
Amsterdam, Beulah. “Mirror Self-Image Reactions before Age Two.” Developmental Psychobiology, vol. 5, no. 4, 1972, pp. 297–305, https://doi.org/10.1002/dev.420050403.
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Meuhlheuser notes that this so-called ‘detour behaviour’ is suggested as a potentially conscious-indicating features (PCIF) in Rial et al., 2007.
The detour behaviour represents the ability of an animal to reach a goal by moving round an interposed obstacle with temporal loss of sensorial contact… The acquisition of “object constancy” in the human child, i.e., the ability to understand that an object temporally hidden is the same after being retrieved, has received considerable attention… Similarly, the detour behaviour requires the maintenance of a memory of the location of a disappeared object, that is, an internal representation of the environment and the production of a “mental” experiment as the animal should construct a complex motor trajectory in advance to the final behavioural performance.
Rial, R. V. et al. “The Evolution of Consciousness in Animals.” Consciousness Transitions: Phylogenetic, Ontogenetic, and Physiological Aspects, Elsevier, 2007, pp. 45–76, https://doi.org/10.1016/B978-044452977-0/50004-8.
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Play including sparring, frolicking, running, jumping, and playing with objects have all been observed in chickens.
From Baxter et al., 2018:
Sparring is an immature version of adult fighting, in which birds act out components of adult aggression such as jumping, kicking and pecking, but without forceful contact or injury (Guhl, 1958). Sparring behaviours develop in young chicks several weeks before aggressive fighting is seen (Guhl, 1958; Dawson and Siegel, 1967) and their frequency is not predictive of later aggression in broilers (Mench, 1988).
…Frolicking develops before sparring and is an apparently functionless behaviour in young fowl that is rarely seen after week 10 (Guhl, 1958; Dawson and Siegel, 1967). When frolicking, chicks will perform a spontaneous burst of running, with wing-flapping and rapid direction changes (Guhl, 1958; Dawson and Siegel, 1967). Frolicking resembles an escape reaction but without the apparent stimulus, and is a contagious behaviour, with one frolicking bird stimulating frolicking in others (Guhl, 1958). An increase in both frolicking and sparring was noted when there was a disturbance, for example, a loud noise or turning on the lights (Guhl, 1958; Dawson and Siegel, 1967). Dawson (1962) noted that there was an initial suppression of activity until the perceived danger (loud noise) had passed, and then an abrupt increase in frolicking and sparring. This is consistent with several species that show an increase in play following some environmental disturbance (reviewed in Špinka et al., 2001).
…The main aims of this paper were to explore the effect of increasing environmental complexity on broiler emotional state, measured through levels of play and avoidance behaviours, and whether these enrichments would additionally have an impact on activity levels away from enrichments.
…Disturbing the broilers and creating space appeared to be an effective method of stimulating frolicking and sparring, and may be a suitable method for investigating these behaviours further.
From Lundén et al., 2022:
Play behaviour occurs in different categories and can be broadly divided into object play (involving manipulation of different items), locomotor play (e.g., running, jumping, frolicking), and social play (e.g., sparring, wrestling). Play in young chickens were described by Kruijt in his account of the ontogeny of social behaviour in Red Junglefowl and some differences between chicken breeds in the occurrence of play behaviour such as running and frolicking have been observed, suggesting a genetic basis for variation in play. Only a few studies have systematically analysed play in young chickens as a means to assess their welfare, and these studies have mainly concerned fast-growing broilers.
…Each test session lasted for 30 min and during this time the behaviour was recorded through overhead video cameras. Ten minutes into the test, a fake worm made of rubber was presented to the birds, via a small opening with a lid in one corner of the arena, ensuring that the birds did not see the person entering the object. During the first two test days, a fake worm measuring 2 × 60 mm was used, and this was then replaced with a larger one (3 × 165 mm) that was used throughout the rest of the testing period. After an additional 10 min, a small cardboard box with three live mealworms were inserted in the arena through a similar small opening in the opposite corner.
From the videos, the occurrence of 14 different play behaviours was scored, and these were subsequently grouped into three larger categories: locomotor play, social play and object play. Furthermore, all occurrences of any behaviour were summed into one category called “Total play”. Locomotor play included running, frolicking, wing flapping, spinning, and spinning while wing flapping. Object play included object running, worm running, object/worm chasing, object/worm exchange and worm pecking. Social play included sparring jumping with or without contact, sparring stand-off with or without contact.
…In conclusion, we found that play in chickens peaks between 25 and 40 days of age and is dominated by object play. Furthermore, although there were no qualitative differences in the types of play behaviour performed, domesticated chickens engaged more in play than ancestral Red Junglefowl, and early stress tended to increase the frequency of play in a stimulating play arena. Future studies should investigate the possibilities of improving the welfare of chickens in the egg production by stimulating play during early ontogeny.
Baxter, M., et al. “Play Behaviour, Fear Responses and Activity Levels in Commercial Broiler Chickens Provided with Preferred Environmental Enrichments.” Animal, vol. 13, no. 1, 22 May 2018, pp. 171–179, https://doi.org/10.1017/s1751731118001118.
Gabrielle, Lundén, et al. “Play Ontogeny in Young Chickens Is Affected by Domestication and Early Stress.” Scientific Reports, vol. 12, no. 1, Aug. 2022, https://doi.org/10.1038/s41598-022-17617-x.
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See Caughey, 2023.
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According to Rethink Priorities’ welfare range estimates literature review (see the sheet “Proxy references,” cell C35):
The ability to use (and in some species, make) tools has been found across a number of animals, including birds, such as corvids, parrots, woodpecker finches, egyptian vultures and herons, most frequently in foraging contexts (e.g. Emery and Clayton, 2009; Ruxton and Hansell, 2010). However, to our knowledge, there does not appear to be published reports of tool-use (experimental or observational) in chickens or closely related species. There does not appear to be published evidence of reports/observations or aims to test tool-use in chickens or closely related species.
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Roosters pass a version of the mirror test, but not the conventional one. From Hillemacher et al., 2023:
Mirror self-recognition (MSR) is often considered a signature of self-awareness… Self-directed behavior occurring only and spontaneously in the mark-and-mirror-condition is assumed to indicate self-recognition. When first exposed to a mirror, most animals show social responses towards their mirror image like acting aggressively towards a conspecific [3]. In chimpanzees, social responses often decline with increasing time of mirror exposure, while contingent and spontaneous self-related behaviors increase in parallel [20]. This transition from social to self-directed behavior is an important component of MSR. Subsequently, a mark (only visible in a mirror) is applied to the animal’s face or body. Behaviors directed to this mark are then interpreted as mark- and thus self-directed behavior and hence as a final proof of MSR. Control conditions include invisible sham marks matching the methodology of the application.
The last decade witnessed increasing controversies about the mark test… Therefore, we propose that MSR experiments should be embedded into the context of a species’ ecological behavior [11, 31]. To this end, we used the alarm calling behavior and the corresponding audience effect as a natural behavioral pattern of chicken [32]. Typically, roosters react to the presence of a predator with an alarm call [33], depending on the predator as well as on the audience: different alarm calls for aerial and terrestrial predators are used [34] and roosters emit alarm calls most likely when they can warn an audience of females that could be mated or genetically related males [32, 35]. When they are alone or if there is a rivaling, non-related conspecific rooster, they will keep silent and thus reduce their own risk of being preyed [33].
…Our data shows that chickens emit significantly more alarm calls in front of a conspecific than in front of a mirror. Hereby, the number of calls emitted in the mirror condition was as low as when the rooster was alone, with no audience present. This cognitive differentiation seemed to depend on visual and not olfactory or auditory input since the animals with a conspecific behind the mirror also did not elicit more alarm calls.
Our chicken failed the classic mark-and-mirror test. But the mark test is only the final part of the procedures to probe the existence of MSR. Before it is applied, the development of self-related behaviors based on transitions from social behavior to contingency testing is usually observed in chimps in front of the mirror [3, 56]. We did not observe such a transition during mirror habituation sessions. Social behaviors like crowing, time spent in front of the mirror, fights towards the mirror, behavior associated with contingency testing like head shaking, and the preening of body parts occurred equally frequent during all habituation sessions, irrespective of the presence of a mirror or the course over time… Based on our results, we cannot completely rule out if our chickens regarded their mirror image as a strange conspecific that does not act “normal” and thus did not warn it. This question should be addressed in future research.
Hillemacher, Sonja, et al. “Roosters Do Not Warn the Bird in the Mirror: The Cognitive Ecology of Mirror Self-Recognition.” PubMed, vol. 18, no. 10, National Institutes of Health, Jan. 2023, pp. e0291416–16, https://doi.org/10.1371/journal.pone.0291416.
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Successful detour behaviour has been observed across multiple studies by Lucia Regolin, Goirgio Vallortigara, and Mario Zanforlin. We’re not aware of any independent replications, but other studies on what affects this behaviour have been done, such as Wichman et al., 2009 (looking at the effects of light exposure of the embryo on detour behaviour) and Sun et al., 2010 (looking at the effects of prenatal morphine exposure on detour behaviour). This suggests the basic behaviour replicates.
Let’s look at the experimental setup of the Regolin et al. studies in more detail. First, Regolin et al., 1994:
The effects of goal visibility and distance on detour behaviour in 2-day-old chicks, Gallus gallus domesticus, were investigated. Cagemates were used as goals and placed behind barriers that concealed them to various degrees. Times needed to develop itineraries to pass round the barrier between the chick and the goal decreased with decreased visibility and increased distance of the goal. Under similar conditions of physical concealment of the goal, however, vertical-bar barriers took longer to negotiate than horizontal-bar barriers. Disocclusion of the goal mediated by the animal’s movements did not seem entirely to account for this asymmetry: chicks seemed to have difficulty in considering vertical bars that concealed a goal as natural obstacles. Visual interaction between cagemates used as goals made the task easier, whereas the number of cagemates visible behind the barrier had no effect.
Second, Regolin at al., 1995a:
Two-day-old chicks, Gallus gallus domesticus, were tested in a detour situation requiring them to abandon a clear view of a desired goal (a small red object on which they had been imprinted) in order to achieve that goal. The chicks were placed in a closed corridor, at one end of which was a barrier with a small window through which the goal was visible. Two symmetrical apertures placed midline to the corridor allowed the chicks to adopt routes passing around the barrier. After entering the apertures, chicks showed searching behaviour for the goal and appeared able to localize it, turning either right or left depending on their previous direction of turn. Thus, in the absence of any local orienting cues emanating from the goal, chicks were aware of the existence of an object that was no longer visible and could represent its spatial localization in egocentric coordinates.
Third, Regolin et al., 1995b:
Chicks, Gallus gallus domesticus, of 2 and 6 days of age were presented with a goal-object that was made to disappear behind one of two screens opposite each other. Chicks proved able to choose the correct screen when the goal-object was a social partner (i.e. a red ball on which they had been imprinted), whereas they searched at random behind either screen when the goal-object was a palatable prey (i.e. a mealworm). Chicks, however, appeared able to make use of the directional cue provided by the movement of the mealworm when tested in the presence of a cagemate. These results suggest that previous failure to obtain detour behaviour in the double screen test in the chick was not due to a cognitive limitation, but rather to the evocation of fear responses to the novel environment that interfered with the correct execution of the spatial task.
Regolin, Lucia, et al. “Perceptual and Motivational Aspects of Detour Behaviour in Young Chicks.” Animal Behaviour, vol. 47, no. 1, Jan. 1994, pp. 123–131, https://doi.org/10.1006/anbe.1994.1014.
Regolin, Lucia, et al. “Object and Spatial Representations in Detour Problems by Chicks.” Animal Behaviour, vol. 49, no. 1, Jan. 1995, pp. 195–199, https://doi.org/10.1016/0003-3472(95)80167-7.
Regolin, Lucia, et al. “Detour Behaviour in the Domestic Chick: Searching for a Disappearing Prey or a Disappearing Social Partner.” Animal Behaviour, vol. 50, no. 1, July 1995, pp. 203–211, https://doi.org/10.1006/anbe.1995.0232.
Wichman, A., et al. “Visual Lateralization and Development of Spatial and Social Spacing Behaviour of Chicks (Gallus Gallus Domesticus).” Behavioural Processes, vol. 81, no. 1, May 2009, pp. 14–19, https://doi.org/10.1016/j.beproc.2008.12.006.
Sun, Huaying, et al. “Detour Behavior Changes Associated with Prenatal Morphine Exposure in 11-Day-Old Chicks.” International Journal of Developmental Neuroscience, vol. 28, no. 3, May 2010, pp. 239–243, https://doi.org/10.1016/j.ijdevneu.2010.02.001.
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According to Horback, 2014:
Play has primarily been described in young piglets and is assessed via the occurrence of specific play markers. These play markers include overt bursts of energy like scamper, or more subtle social behaviors like nose-to-body contact. This review describes four areas of play for swine: locomotor, object, sow-piglet, and, peer play. From sporadic leaping to combative wrestling, play behavior allows for the fine-tuning of reflexive behavior which can enhance physical development, enrich cognitive abilities, and facilitate the maintenance of social bonds.
Play in pigs is sufficiently accepted that studies have been conducted on what affects it, for example, Donaldson et al., 2002, and Steinerová, et al., 2024.
Horback, Kristina. “Nosing Around: Play in Pigs.” Animal Behavior and Cognition, vol. 2, no. 2, 2014, p. 186, https://doi.org/10.12966/abc.05.08.2014.
Donaldson, Tammy M, et al. “Effects of Early Play Experience on Play Behaviour of Piglets after Weaning.” Applied Animal Behaviour Science, vol. 79, no. 3, Nov. 2002, pp. 221–231, https://doi.org/10.1016/s0168-1591(02)00138-7.
Karolína Steinerová, et al. “The Promotion of Play Behaviour in Grow-Finish Pigs: The Relationship between Behaviours Indicating Positive Experience and Physiological Measures.” Applied Animal Behaviour Science, 1 Apr. 2024, pp. 106263–106263, https://doi.org/10.1016/j.applanim.2024.106263.
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There are many accounts of pig grief, but no clear scientific studies.
According to Pribac, 2013:
Accounts of other nonhuman animals exhibiting signs of deep grief at the death of a proximal subject are not unusual, and they include chicks, cows (Hatkoff), pigs and many other species. A substantial collection of stories of nonhuman animals grieving appears in Barbara
King’s recent book How Animals Grieve.
…Cases of an animal’s grief ending with his or her own death are also known. One such example is Damini, an elephant in an Indian zoo, reported by BBC News on 6 May 1999 as having starved herself to death after her friend had died in childbirth. A similar episode almost occurred at the Edgar’s Mission Farm Sanctuary in Australia, in 2010. When Daisy, a pig, died, her close companion, Alice, lay on her grave for two days and nights, refusing to eat or move (Ahern, personal communication).
McGrath et al., 2013, notes:
However, there have been no scientific studies on any of the farm animals discussed above (cows, pigs, sheep or goats) which have resulted in evidence for a two-stage protest-despair response characteristic of grief. This may be due to the fact that these are prey animals and therefore a period of withdrawal or inactivity could compromise their survival. In addition, there has been no systematic investigation into the long-term reactions to extensive separation periods. Despite this, there is ample evidence that these animals do experience distress, and the results of our survey suggest that the public are aware of this.
Brooks Pribac, Teja. “Animal Grief.” Animal Studies Journal, vol. 2, no. 2, 1 Jan. 2013, pp. 67–90, ro.uow.edu.au/asj/vol2/iss2/5/.
McGrath, N, et al. “Public Attitudes towards Grief in Animals.” Animal Welfare, vol. 22, no. 1, 1 Feb. 2013, pp. 33–47, https://doi.org/10.7120/09627286.22.1.033.
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Tool use has been observed in the Visayan warty pig (Sus cebifrons), a close relative to the domestic pig.
Root-Berstein et al., 2019:
Tool use has been reported in a wide range of vertebrates, but so far not in Suidae (the pigs). Suidae are widely considered to be “intelligent” and have many traits associated with tool use, so this is surprising. Here, we report the first structured observations of umprompted instrumental object manipulation in a pig, the Visayan warty pig Sus cebifrons, which we argue qualifies as tool use. Three individuals were observed using bark or sticks to dig with. Two individuals, adult females, used the sticks or bark, using a rowing motion, during the final stage of nest building. The third individual, an adult male, attempted to use a stick to dig with. Stick and branch manipulation was observed in other contexts, but not for digging. Our observations suggest the hypothesis that the observed use of stick to dig with could have been socially learned through vertical transmission (mother-daughter) as well as horizontal transmission (female-male).
Root-Bernstein, Meredith, et al. “Context-Specific Tool Use by Sus Cebifrons.” Mammalian Biology, vol. 98, 1 Sept. 2019, pp. 102–110, https://doi.org/10.1016/j.mambio.2019.08.003.
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We didn’t find any studies showing this failure, but they’re not on any lists of animals that pass the test
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According to Jansen et al., 2008:
Pigs were then placed individually in the maze, and social reinstatement proved to be a strong incentive to find the exit leading to the home pen. We subsequently blocked the direct route to the exit, forcing animals to find a detour (memory test 1, MT1). This test was repeated once to investigate the relative improvement, i.e. detour learning (memory test 2, MT2)… Performance was substantially improved in MT2, indicating that once a goal is apparent, pigs are able to solve a complex spatial memory task easily.
Jansen, Jarno, et al. “Spatial Learning in Pigs: Effects of Environmental Enrichment and Individual Characteristics on Behaviour and Performance.” Animal Cognition, vol. 12, no. 2, Sept. 2008, pp. 303–15, https://doi.org/10.1007/s10071-008-0191-y.
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There are a large number of anecdotal observations of fish play, outlined in Burghardt, 2005, but no clear studies of the subject.
If you want to know more you can read the full chapter of Burghardt here.
Burghardt, Gordon M. “The Origins of Vertebrate Play: Fish That Leap, Juggle, and Tease.” The Genesis of Animal Play: Testing the Limits, by Gordon M. Burghardt, Cambridge, Mass., The MIT Press, 4 Feb. 2005, pp. 309–358.
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It’s clear that some fish use tools; for example, wrasse use rocks to help break open prey. You can watch videos of fish doing this.
According to Brown, 2012, observations of tool use have also been made in cichlids and whitetail majors.
It’s very unclear that this says anything about the fish commonly farmed — although wrasse are used in farms to help keep species like salmon free from sea lice.
Brown, Culum. “Tool Use in Fishes.” Fish and Fisheries, vol. 13, no. 1, 24 Nov. 2011, pp. 105–115, https://doi.org/10.1111/j.1467-2979.2011.00451.x.
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Kohda et al., 2019, conducted the mirror self-recognition test on cleaner wrasse (Labroides dimidiatus).
We found that (1) ¹⁴⁄₁₄ new individuals scraped their throat when a brown mark had been provisioned, but only in the presence of a mirror; (2) blue and green color marks did not elicit scraping; (3) intentionally injecting the mark deeper beneath the skin reliably elicited spontaneous scraping in the absence of a mirror; (4) mirror-naive individuals injected with a brown mark scraped their throat with lower probability and/or lower frequency compared to mirror-experienced individuals; (5) in contrast to the mirror images, seeing another fish with the same marking did not induce throat scraping; and (6) moving the mirror to another location did not elicit renewed aggression in mirror-experienced individuals. Taken together, these results increase our confidence that cleaner fish indeed pass the mark test, although only if it is presented in ecologically relevant contexts.
Even more impressively, later work by Kohda et al., 2023, found that cleaner wrasse recognise themselves by looking at their mirror-image face.
Some animals have the capacity for mirror self-recognition, but implications for self-awareness remain controversial. Here, we show that cleaner fish, Labroides dimidiatus, likely recognize their own mirror image using a mental image of the self-face comparable to humans. Mirror-naïve fish frequently attacked photographs of both themselves and strangers. In contrast, after passing the mirror test, aggression against their own photograph and composite photographs of own face/stranger body declined, but aggression remained toward unfamiliar and composite photographs of stranger face/own body. Our results suggest that cleaner fish with MSR ability can recognize their own mirror image based on a mental image of their own face, rather than by comparing body movements in the mirror.
Kohda, Masanori, et al. “Further Evidence for the Capacity of Mirror Self-Recognition in Cleaner Fish and the Significance of Ecologically Relevant Marks.” PLOS Biology, vol. 20, no. 2, 17 Feb. 2022, p. e3001529, https://doi.org/10.1371/journal.pbio.3001529.
Kohda, Masanori, et al. “Cleaner Fish Recognize Self in a Mirror via Self-Face Recognition like Humans.” Proceedings of the National Academy of Sciences, vol. 120, no. 7, 6 Feb. 2023, https://doi.org/10.1073/pnas.2208420120.
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According to Sovrano et al., 2018:
Four species of fish (Danio rerio, Xenotoca eiseni, Carassius auratus, and Pterophyllum scalare) were tested in a detour task requiring them to temporarily abandon the view of the goal-object (a group of conspecifics) to circumvent an obstacle. Fishes were placed in the middle of a corridor, at the end of which there was an opaque wall with a small window through which the goal was visible. Midline along the corridor two symmetrical apertures allowed animals to access two compartments for each aperture. After passing the aperture, fishes showed searching behavior in the two correct compartments close to the goal, appearing able to localize it, although they had to temporarily move away from the object’s view. Here we provide the first evidence that fishes can solve such a detour task and therefore seem able to represent the “permanence in existence” of objects, which continue to exist even if they are not momentarily visible.
Valeria Anna Sovrano, et al. “A Detour Task in Four Species of Fishes.” Frontiers in Psychology, vol. 9, Frontiers Media, Nov. 2018, https://doi.org/10.3389/fpsyg.2018.02341.
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According to Mirwan et al., 2015, bees exhibit a form of detour behaviour (not unlike the behaviour we considered in other animals — moving around obstacles to reach a goal even when they temporarily can’t sense the goal):
We therefore trained bumblebees with two types of task that we believe represented challenges unlike any they have evolved to respond to. These involved dragging various-sized caps aside and rotating discs through varying arcs away from the entrances of artificial flowers (via detours of up to three body lengths), to access a reward hidden beneath. Further, we successfully trained bees to use disc colour as a discriminative stimulus predicting whether rotating discs clockwise or counterclockwise would reveal the reward. This true, complex operant conditioning demonstrated that bumblebees can learn novel, arbitrary behavioural sequences, manipulating and moving items in ways that seem far from any natural task that they would encounter, and doing so flexibly in response to specific discriminative stimuli. This adds to growing evidence of impressive behavioural plasticity and learning abilities in bees, and suggests new approaches for probing their cognitive abilities in the future.
Mirwan, H. B., et al. “Complex Operant Learning by Worker Bumblebees (Bombus Impatiens): Detour Behaviour and Use of Colours as Discriminative Stimuli.” Insectes Sociaux, vol. 62, no. 3, 9 June 2015, pp. 365–377, https://doi.org/10.1007/s00040-015-0414-6.
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In a now widely-cited study, Bateson et al., 2011, conducted experiments on honeybees to see how they responded to vigorous shaking designed to simulate a predatory attack. They showed that bees were more likely to withhold their mouthparts from ambiguous test odours after such an attack, suggesting that the negative episode was causing them to more readily interpret future events as bad or dangerous.
Here, we ask whether honeybees display a pessimistic cognitive bias when they are subjected to an anxiety-like state induced by vigorous shaking designed to simulate a predatory attack. We show for the first time that agitated bees are more likely to classify ambiguous stimuli as predicting punishment. Shaken bees also have lower levels of hemolymph dopamine, octopamine, and serotonin. In demonstrating state-dependent modulation of categorization in bees, and thereby a cognitive component of emotion, we show that the bees’ response to a negatively valenced event has more in common with that of vertebrates than previously thought.
…Using the best criteria currently agreed on for assessing animal emotions, i.e., a suite of changes in physiology, behavior, and especially cognitive biases [4–8], we have shown that agitated bees display a negative emotional state. Although our results do not allow us to make any claims about the presence of negative subjective feelings in honeybees, they call into question how we identify emotions in any nonhuman animal. It is logically inconsistent to claim that the presence of pessimistic cognitive biases should be taken as confirmation that dogs or rats are anxious but to deny the same conclusion in the case of honeybees.
Bateson, Melissa, et al. “Agitated Honeybees Exhibit Pessimistic Cognitive Biases.” Current Biology, vol. 21, no. 12, June 2011, pp. 1070–1073, https://doi.org/10.1016/j.cub.2011.05.017.
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Yang et al., 2013, found that flies experiencing uncomfortable heat will try to walk away — but when they find they can’t do that, they will walk around more slowly and take longer and more frequent rests.
In a wide range of animals, uncontrollable stressful events can induce a condition called “learned helplessness.” In mammals it is associated with low general activity, poor learning, disorders of sleep and feeding, ulcers, and reduced immune status, as well as with increased serotonin in parts of the brain. It is considered an animal model of depression in humans. Here we investigate learned helplessness in Drosophila, showing that this behavioral state consists of a cognitive and a modulatory, possibly mood-like, component. A fly, getting heated as soon as it stops walking, reliably resumes walking to escape the heat. If, in contrast, the fly is not in control of the heat, it learns that its behavior has no effect and quits responding. In this state, the fly walks slowly and takes longer and more frequent rests, as if it were “depressed.” This downregulation of walking behavior is more pronounced in females than in males.
Ries et al., 2017, found that this state was affected by antidepressants:
Major depressive disorder (MDD) affects millions of patients; however, the pathophysiology is poorly understood. Rodent models have been developed using chronic mild stress or unavoidable punishment (learned helplessness) to induce features of depression, like general inactivity and anhedonia. Here we report a three-day vibration-stress protocol for Drosophila that reduces voluntary behavioural activity. As in many MDD patients, lithium-chloride treatment can suppress this depression-like state in flies.
Yang, Zhenghong, et al. “Flies Cope with Uncontrollable Stress by Learned Helplessness.” Current Biology, vol. 23, no. 9, May 2013, pp. 799–803, https://doi.org/10.1016/j.cub.2013.03.054.
Ries, Ariane-Saskia, et al. “Serotonin Modulates a Depression-like State in Drosophila Responsive to Lithium Treatment.” Nature Communications, vol. 8, 6 June 2017, https://doi.org/10.1038/ncomms15738.
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Loukola et al., 2017, found that bees were able to use balls to gain a reward:
We explored bees’ behavioral flexibility in a task that required transporting a small ball to a defined location to gain a reward. Bees were pretrained to know the correct location of the ball. Subsequently, to obtain a reward, bees had to move a displaced ball to the defined location. Bees that observed demonstration of the technique from a live or model demonstrator learned the task more efficiently than did bees observing a “ghost” demonstration (ball moved via magnet) or without demonstration. Instead of copying demonstrators moving balls over long distances, observers solved the task more efficiently, using the ball positioned closest to the target, even if it was of a different color than the one previously observed.
Loukola, Olli J., et al. “Bumblebees Show Cognitive Flexibility by Improving on an Observed Complex Behavior.” Science, vol. 355, no. 6327, 23 Feb. 2017, pp. 833–836, https://doi.org/10.1126/science.aag2360.
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Araujo et al., 2021, put Drosophila melanogaster into a ‘chronic unpredictable mild stress’ (CUMS) environment.
To implement the CUMS paradigm, flies were subjected to various stressors in a chronic and unpredictable manner according to a randomized scheme over a period of 10 days described by (Araujo et al., Citation2018). Stressors in the CUMS regimen were based on previously described protocol including: (a) cold stress (0 °C, 30 min; adapted (Araujo et al., Citation2018), (b) starvation stress (5% sucrose on the paper filter for 58 h), (c) heat stress (36 °C, 4 h) and (d) sleep deprivation (light/dark cycle inversion). In (b) the flies of the ORY and FLX groups continued to receive treatment on the filter paper for 58 h.
They then treated flies with γ-Oryzanol, which appears to have an antidepressant effect in mice, and found that it prevented CUMS.
We hypothesized that ORY could exhibit antidepressant properties in widely accepted predictive models of depression, such as forced swim testing, sucrose preference testing, and other behavioral tests used to screen for new antidepressant drugs.
…The objective of this work was to evaluate the possible antidepressant effect of ORY in the depressive model induced by CUMS in male Drosophila melanogaster. ORY protected against the deleterious effects of CUMS by not exhibiting obvious neurochemical behaviors and changes, predictive of depressive behavior.
Araujo, Stífani Machado, et al. “γ-Oryzanol Produces an Antidepressant-like Effect in a Chronic Unpredictable Mild Stress Model of Depression in Drosophila Melanogaster.” Stress (Amsterdam, Netherlands), vol. 24, no. 3, 1 May 2021, pp. 282–293, https://doi.org/10.1080/10253890.2020.1790519.
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More comprehensive attempts can be found in Meuhlhauser’s report and the “Proxy references” sheet of this spreadsheet put together by Rethink Priorities.
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For more, see “My overall thoughts on PCIF arguments” in Meuhlhauser, 2017.
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Unless humans have conscious subsystems, which is not a common view.
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Meuhlheuser tries a few methods beyond PCIFs to investigate animal consciousness.
He considers whether we can find any necessary or sufficient conditions for consciousness. He investigates the view that a cortex is required for consciousness), but doesn’t come to any clear conclusions.
Meuhlhauser also addresses some big-picture considerations on how rare consciousness is. For example, he investigates whether, for all behaviours that arise from conscious systems, there is the possibility that an unconscious system could behave the same way. If there is, it’s much harder to find evidence for consciousness. He also investigates how complex we should consider consciousness to be: if it’s more complex, we should think it’s less likely.
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We don’t necessarily have to reject the idea of binary moral status in order to do this — we could assign moral status to neurons themselves rather than to individuals. I don’t know of any philosophers who have argued for this position.
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Cow neuron counts from Vertebrate Neuron counts by Jaoa Fabiano — for other data, see the table above.
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According to Shriver in What neural counts can and can’t tell us about moral weight:
For there also are a large number of studies showing an inverse relationship between brain volume and the intensity of particular affective states. In particular, when it comes to chronic pain, by far the most commonly cited relationship between brain volume and chronic pain is a decrease in brain volume in regions commonly associated with the experience of pain. For example, see the Davis et al. (2008) article “Cortical thinning in IBS: implications for homeostatic, attention, and pain processing.”
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The Rethink Priorities’ Moral Weight Project tried to come up with quantitative estimates of the probability of consciousness for various species.
They considered 53 potentially consciousness-indicating features and assessed (based on the academic literature) the chances that each of 23 different species have each feature. You can see all 1,219 judgements in this spreadsheet.
They then looked at the proportion of the features each animal has compared to humans and considered 16 different ways of using these proportions to come to probability estimates, by doing things like:
- Where they’re uncertain, weighting each feature by a score depending on the probability the animal has that feature
- Using different mathematical functions, like comparing the cubes of sums instead of pure sums
- Weighting each feature by the value various team members judged it to have (for example some team members focused on features relating to nociception)
- Looking at the proportion of features that seem to, at times or to some extent, function unconsciously in humans and comparing to that figure as a check on the validity of the features used
- Considering some subjective prior probabilities that Rethink Priorities researchers had previously laid out, and using the proportions as evidence to update these probabilities
You can see the calculations for yourself for 11 of these in this spreadsheet, and the calculations for the final five methods (using prior probabilities and updating) are set out in this document.
None of these methods are perfect — ultimately, only the method using prior probabilities seems to us to have some mathematical justification, but even then the introduction of these prior probabilities makes the results far more subjective.
The initial 11 gave results like this:

The methods that gave lower estimates of the probability of consciousness (cubic and power 4) looked at the third or fourth power of the proportion of features rather than just the proportion. Since these proportions are all less than one, this resulted in lower estimates. In effect, these methods are saying something like “maybe you need almost all of these features to be conscious,” rather than treating each feature as some independent evidence.
It’s worth noting that there are some confusing things in the graph — like estimates for fruit flies being so high. (This is because where there was no evidence for a feature, the researchers assumed that it was absent and fruit flies are extremely well-studied compared to other species). Overall, though, these estimates suggest that we can meaningfully claim that pigs are more likely to be conscious than fish.
For the final, subjective probability method, the team carried out a Monte Carlo simulation to provide some sense of the uncertainty of the estimates. This graph shows what they found:

The red lines show the ‘priors’: the probabilities that the team had before looking at the data. The blue lines show ‘posteriors’: the updated probabilities and uncertainty estimated with the Monte Carlo simulations.
The two main takeaways from this graph are:
- The large error bars — these estimates are hugely uncertain.
- The clear similarity between the priors and the posteriors — ultimately, we only have weak evidence here, so these results are extremely subjective.
The ordering of animals in these results fit with my intuitions better; fruit flies are less likely to be conscious, while octopuses are more likely to be conscious.
Overall, we think that weighting each individual by the probabilities estimated here would be a reasonable way to count animals, in large part because there doesn’t seem to be a better or more authoritative way yet. But it’s worth re-emphasising that these estimates are subjective and highly uncertain.
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You can find all the data used, and all 12 model results, here.
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The researchers carried out a Monte Carlo simulation. They carried out 10,000 runs of the simulation for each model. Details of the methodology can be found here.
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They used the critical flicker-fusion frequency — the threshold at which a rapidly flickering light appears to glow steadily — to measure this effect.
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They modelled each distribution as normal or lognormal depending on the skew, assigned each model equal probability of being correct, and sampled from these distributions.
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Note these results, which include the neuron count model, are from table 6 in this document. These differ slightly from the headline results in Bob Fischer’s blog post, which exclude the neuron count model.
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In some cases (shrimp and octopuses), the upper errors go higher than for humans — we’d guess this mainly represents how little we know about these species (and is an artefact of the way uncertainty was simulated). When we spoke to one of the researchers, they suggested this is likely because of the ‘subjective experience of time’ adjustment. In the case of shrimp, it’s worth noting how low the median value is: a full 50% of the probability is that the value for shrimp is smaller than that cross.
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Much of the initiative behind insect farming is based around the idea that insects are a more sustainable option than other food sources. We’re sceptical of this claim. According to a preprint literature review by Biteau et al., 2024a:
Many of the benefits commonly mentioned by companies and proponents of insect farming are challenged by current scientific evidence… There are significant uncertainties, with many authors highlighting the fact that the future environmental impact of large-scale insect production is largely unknown. This is especially true given claims that insects can be fed on food waste and that insect frass can be used as fertiliser, both of which have considerable challenges to overcome at scale. Lastly, most insect based foods replace plant-based products with limited environmental impact rather than meat, and several studies indicate that insects-based feeds and pet food can have a larger environmental impact than conventional products.
A core claim here is that feeding insects food waste is difficult. In a peer-reviewed literature review by Biteau et al., 2024b:
While the idea of turning trash into treasure for insect agriculture may be appealing in theory, the reality appears to be more challenging. Only some species of insects can be farmed using food waste, while others perform poorly. The inconsistent availability and quality of food waste pose significant obstacles to the establishment of large-scale insect farms aimed at consistently yielding high-quality products. Consequently, insect-farming companies often resort to utilising high-quality feeds already in demand by other sectors. Moreover, competition intensifies for the limited pool of food waste suitable for insect agriculture, as various industries, including agriculture, aquaculture, pet food production, and biogas manufacturing, vie for the same resources. Additionally, concerns regarding food safety due to contamination risks constrain the types of food waste viable for insect cultivation.
Corentin Biteau, et al. Have the Environmental Benefits of Insect Farming Been Overstated? A Critical Review. 4 Apr. 2024, https://doi.org/10.32942/x2w60r.
Corentin Biteau, et al. “Is Turning Food Waste into Insect Feed an Uphill Climb? A Review of Persistent Challenges.” Sustainable Production and Consumption, 1 July 2024, https://doi.org/10.1016/j.spc.2024.06.031.
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See table S1 from Whitton et al., 2021.
Meat consumption per capita fell from 2000 to 2019 in six investigated countries: Canada, Ethiopia, New Zealand, Nigeria, Paraguay, and Switzerland.
It’s plausible that the explanation in Canada, New Zealand, and Switzerland is related to income per capita.
Animal Ask investigated the declines in developing countries (Paraguay, Ethiopia and Nigeria). In Paraguay, they note that “the decline is mostly due to rising beef exports, which only correspond to a domestic, not international, decline in meat consumption.” In Ethiopia and Kenya, they note that “the decline is likely due to the 2011 East African Drought.”
Whitton, Clare, et al. “Are We Approaching Peak Meat Consumption? Analysis of Meat Consumption from 2000 to 2019 in 35 Countries and Its Relationship to Gross Domestic Product.” Animals, vol. 11, no. 12, 6 Dec. 2021, p. 3466, https://doi.org/10.3390/ani11123466.
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This is only a median scenario — the UN thinks there’s around a 40% chance that the global population won’t start to decrease this century.
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One source of evidence for this is the so-called “meat paradox,” as discussed in a review paper by Gradidge, et al. (2021):
The ‘meat paradox’ (MP) is the phenomenon of people using animals in ways that harm them (e.g., meat consumption), despite caring for animals and wishing them no harm (Loughnan et al., 2014)1. This theoretical MP represents a form of cognitive dissonance (hereon dissonance), describing the discomfort arising from a contradiction between one’s beliefs and behaviours (Loughnan et al., 2014). For instance, most US participants (n = 1,024) are very or somewhat concerned about animal welfare across contexts (e.g., research, 67%; zoos, 57%; food production, 54%; Riffkin, 2015), indicating most people care about animals. In fact, people empathise more with dogs than adult human victims (Levin et al., 2017). Yet, even though care for animals sometimes exceeds care for humans, 90-97% of people consume meat (Food Standards Agency [FSA], 2012; The Vegan Society [TVS], 2019)… most articles within this review directly or indirectly supported the MP (70 articles; 95.89%).
Given that people seem to care for animals, it seems plausible that they would avoid eating meat if doing so were less costly — i.e. if there were better and cheaper alternative products.
Gradidge, Sarah, et al. “A Structured Literature Review of the Meat Paradox.” Social Psychological Bulletin, vol. 16, no. 3, 23 Sept. 2021, https://doi.org/10.32872/spb.5953.
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The main challenges are flavour and texture (see Wang et al., 2022), as well as nutrition, food safety, cost, and consumer confidence (see Ahmad et al., 2022).
For more on the science of plant based meat, take a look at this introduction by the Good Food Institute.
Wang, Yaqin, et al. “Flavor Challenges in Extruded Plant‐Based Meat Alternatives: A Review.” Comprehensive Reviews in Food Science and Food Safety, vol. 21, no. 3, 26 Apr. 2022, https://doi.org/10.1111/1541-4337.12964.
Ahmad, Mudasir, et al. “Plant-Based Meat Alternatives: Compositional Analysis, Current Development and Challenges.” Applied Food Research, vol. 2, no. 2, Dec. 2022, p. 100154, https://doi.org/10.1016/j.afres.2022.100154.
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Humbird, 2020. See table 4.7 for the capital expenditure (CAPEX) and production rate for a fed-patch production facility and table 4.14 for a perfusion process facility.
The facility is assumed to contain 24 bioreactors of 20 m³. This minimises the cost of production within a single facility subject to the physical constraints outlined by the report (see figure 4.4b).
Humbird, David. Scale-up Economics for Cultured Meat: Techno-Economic Analysis and Due Diligence. 29 Dec. 2020, https://doi.org/10.31224/osf.io/795su.
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This report from Jacob Peacock at Rethink Priorities suggests that price, taste, and convenience-competitive plant-based meat would not currently replace meat. We’re a bit more optimistic than that, as we’d guess that if there were clear alternative products, it would be much easier to both push for increased welfare on farms and to convince people to stop eating factory-farmed meat.
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It’s very hard to predict technological changes over the very long run. That said, one way of doing so is to look at fundamental limits. In this case, we can look at the energy efficiency with which animals convert calories in their feed into calories in meat. This calorie efficiency ranges from around 5% (in prawns) to up to 30% (in broiler chickens) (see figure 2 in Fry et al., 2018). While we’ll likely find ways to improve this efficiency (for example, by developing more efficient breeds), it seems fundamentally impossible to grow an animal that moves around and has a complex brain more efficiently than you could grow just the parts you’d want to eat.
Even more precisely, sensory systems — including nociception (neural pathways which cause pain) — use energy. According to Niven and Laughlin, 2008:
Energy consumption affects all aspects of animal life from cellular metabolism and muscle contraction to growth and foraging (Alexander, 1999). Yet despite early studies on energy metabolism in neural tissue (e.g. Kety, 1957), the impact of energy consumption upon the evolution of nervous systems has only recently begun to be generally appreciated (Laughlin, 2001). Recent studies have made substantial advances in relating the energy consumption of neural tissue to neural function. Together these studies show that there are high energetic costs associated with the nervous system both at rest and whilst neurons are signalling (Laughlin et al., 1998; Attwell and Laughlin, 2001; Niven et al., 2007). Crucially for the evolution of the nervous system, and in particular sensory systems, these costs are incurred even during activity. Thus, animals pay an energetic cost associated with [sic] nervous system irrespective of the demands of other tissues such as skeletal muscle.
It doesn’t seem fundamentally impossible to produce meat without the development of these neural pathways, and doing so would be more efficient, so we’d guess that a sufficiently advanced future society would do so. If we can produce meat without sensing, then we would be producing meat without any positive or negative experience.
Fry, Jillian P, et al. “Feed Conversion Efficiency in Aquaculture: Do We Measure It Correctly?” Environmental Research Letters, vol. 13, no. 2, 1 Feb. 2018, p. 024017, https://doi.org/10.1088/1748-9326/aaa273.
Niven, Jeremy E., and Simon B. Laughlin. “Energy Limitation as a Selective Pressure on the Evolution of Sensory Systems.” Journal of Experimental Biology, vol. 211, no. 11, June 2008, pp. 1792–804, https://doi.org/10.1242/jeb.017574.
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This makes slaughter improvements seem particularly likely to be cost-effective interventions. Tomasik even argues that ending animal farming might be bad overall because of the effects on wild animals. (I think this is an interesting argument, but I’m less confident than Tomasik about whether these effects on wild animals would be good or bad overall.)
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According to Open Philanthropy in written correspondence.
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Open Philanthropy spent around $100m on farmed animal welfare in 2023.
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According to Open Philanthropy in written correspondence.
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According to Professor Bob Fischer at Rethink Priorities in written correspondence.
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Perhaps a good rule of thumb is to think of current-day civilization as if we’re holding a baton in a relay race. At some point soon we’re going to hand over that baton to a future generation — and our job is to put those people in the best position possible to improve the long-run future.
I think this is an attractive rule of thumb because it reflects how our uncertainty about how the long-run future will unfold makes it much harder to influence than the present. That’s because, under this rule of thumb, we focus only on the effects of our actions when we have the baton (and when we hand that baton over) — that is, the relatively near future (e.g. the next 100 years).
This rule of thumb suggests that ensuring the next generation exists to take over in the race is crucial (reducing existential risk), but it also seems to support helping them broadly make good decisions, as well as ‘safeguarding’ civilisation while we are responsible for it (which might be taken to include making sure we don’t do anything morally awful). I think this rule of thumb points more toward a larger mix of issues being top priorities than explicit expected value calculations, which points more exclusively toward existential risk reduction.
There are other plausible rules of thumb for identifying particularly important issues to work on (from a longtermist perspective). For example:
- Identify the main process that’s going to substantially affect the future and work on its trajectory. We’d guess this points towards working on improving the trajectory of transformative AI.
- Identify the issues that are most likely to make the future overall bad and try to solve them. We’d guess this points toward a focus on reducing suffering and the structures in society that lead to systematic suffering of morally relevant beings (e.g. solving factory farming).
- Identify the worst thing we’re currently doing and find a way to stop it — especially if stopping it seems unlikely to be reversed. We’d guess this points towards working on factory farming.
It’s hard to know what to conclude from all this. I think the explicit expected value estimate is pretty useful because it’s capturing something important that the other rules of thumb miss (and that society as a whole tends to underrate), but it shouldn’t be treated as the only tool in our toolbox.

Factory farming as a pressing world problem

Summary

Scale

Neglectedness

Solvability

Introduction

How many animals are in farms?

How do we treat these animals?

Farmed chickens

Farmed pigs

Farmed cattle

Farmed sheep and goats

Farmed fish

Farmed frogs and turtles

Farmed shrimp and crustaceans

Other farmed invertebrates (snails and insects)

To what extent do animals deserve our moral consideration?

Animal consciousness and pain

What makes something deserving of moral consideration?

Different moral approaches

How many animals count morally the same as one human?

Counting the number of individuals

Counting the number of neurons

Trying to estimate the probability of consciousness

Using welfare ranges

Interview: Bob Fischer

How might factory farming change in the future?

How will factory farming be affected by technological advances?

When might we develop really good alternatives to meat?

Would a competitive meat alternative end factory farming, and if so — when?

How could AI affect factory farming?

What might happen to factory farming in the very long-run future?

There are promising ways of solving this problem

Work on factory farming is highly neglected

How can we compare the pressingness of factory farming to existential risks?

What are the major arguments against this problem being (especially) pressing?

What can you do to help?

Earning to give

Helping to run nonprofits

Seren Kell

Founding something new

Andrés Jiménez Zorrilla

Government and policy

Corporate campaigning and activism

Leah Garcés

Scientific and engineering research

Strategy research and grantmaking

Lewis Bollard

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Key organisations

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