Ban of day-old chick culling: Ethical concerns and challenges for policy, industry, and research

Worldwide, billions of day-old male chicks are culled each year in the egg industry due to the low market value of layer-type males. As a result of public pressure on this ethical issue, some countries banned the practice, leading to changes in animal welfare legislation. In addition to the use of dual-purpose chicken for egg and meat production, technologies for in-ovo sex determination, aiming to cull male embryos during early development and prior to the onset of pain perception, are feasible alternatives. However, the temporal onset of pain perception in chick embryos is still unknown, and its determination is challenging. Here we embed a review of the existing literature of in-ovo pain research under the country-specific umbrella of societal discussions and culling alternatives. Recently, a study on nociception measured first signs of responses by the embryo at day 13 of incubation. Still, neither the depiction of nociceptive pathways nor an EEG, which includes signals of general muscle contraction, provide definitive proof of the perception of pain. We urge that more knowledge about the development of pain perception in chick embryos is key to the ethical framework that should underpin policy decisions.