Nociception in chicken embryos, Part III: Analysis of movements before and after application of a noxious stimulus

Many potentially noxious interventions are performed on chicken embryos in research and in the poultry industry. It is therefore in the interest of animal welfare to define the point at which a chicken embryo is capable of nociception. The present part III of a comprehensive study examined the movements of developing chicken embryos with the aim of identifying behavioral responses to aww noxious stimulus. For this purpose, a noxious mechanical stimulus and a control stimulus were applied. The recorded movements of the embryos were evaluated using the markerless pose estimation software DeepLabCut and manual observations. After the application of the noxious stimulus, a significant increase in beak movement was identified in 15- to 18-day-old embryos. In younger embryos, no behavioral changes related to the noxious stimulus were observed. The results indicate that noxious stimuli at the beak base evoke a nocifensive reaction in chicken embryos starting at embryonic day 15.