Norwood and Lusk estimate that one cage egg requires 0.003212204 chickens and one cage-free egg requires 0.003229267 chickens (233).
There is actually a typo in the table 8.4 in page 233 on which you are basing this. If you read the text closely, you can see that the value for “Number of non breeder animals associated with one cage egg” should be be 1⁄509 = 0.001964637, not 1⁄314 = 0.003184713. The book does not make the same mistake in a very similar table 8.7.
However, in my opinion, what matters more is how many chicken-years are required per egg. And since cage-free hens seem to live shorter lives, the difference in chicken-years required per egg is not as big as chickens required per egg.
But according to a person with more knowledge, the bigger problem is that the book is comparing industrial cage systems with small-scale cage-free systems that are not using optimal genetics. That is not the relevant comparison for the current situation where large-scale producers are switching to cage-free systems. Numbers that the book uses differ quite a lot from numbers in other sources that are discussing industrial systems.
I have spent two or three weeks looking into these issues and have quite neat document about it that I decided not to publish. If somebody thinks that the information in the document could be action-relevant to them, you can email me at saulius@rethinkpriorities.org and I will send you the document.
There is actually a typo in the table 8.4 in page 233 on which you are basing this. If you read the text closely, you can see that the value for “Number of non breeder animals associated with one cage egg” should be be 1⁄509 = 0.001964637, not 1⁄314 = 0.003184713. The book does not make the same mistake in a very similar table 8.7.
However, in my opinion, what matters more is how many chicken-years are required per egg. And since cage-free hens seem to live shorter lives, the difference in chicken-years required per egg is not as big as chickens required per egg.
But according to a person with more knowledge, the bigger problem is that the book is comparing industrial cage systems with small-scale cage-free systems that are not using optimal genetics. That is not the relevant comparison for the current situation where large-scale producers are switching to cage-free systems. Numbers that the book uses differ quite a lot from numbers in other sources that are discussing industrial systems.
I have spent two or three weeks looking into these issues and have quite neat document about it that I decided not to publish. If somebody thinks that the information in the document could be action-relevant to them, you can email me at saulius@rethinkpriorities.org and I will send you the document.