I asked Google when chicken embryos start to feel pain and this was the first result (i.e. I didn’t look hard and I didn’t anchor on a figure):
A recent study by the Technical University of Munich in Germany measured chicken embryos’ heart rate, brain activity, blood pressure and movements in response to potentially painful stimuli like heat and electricity and concluded that they didn’t seem to feel them until at least day 13. (14 Oct 2023)
I asked Google when chicken embryos start to feel pain and this was the first result (i.e. I didn’t look hard and I didn’t anchor on a figure):