Humane killing of animals implies a painless death (euthanasia). This depends on the rapidity with which unconsciousness is achieved and the maintenance of this state until death occurs. Euthanasia methods for day-old chicks must also be economical and should not interfere with the use of the carcasses for animal food or fertilizer. Manual decapitation or dislocation of the neck are the best available manual methods of euthanasia. For larger numbers of birds, the literature recommends homogenization in a crusher. In the author's own experiments, the destruction of day-old chicks was most effectively carried out by poisoning with carbon dioxide (CO2). A simple gas chamber was constructed, which is now commercially available, into which boxes of chicks were placed. The chamber has the capability to euthanize approximately 8,000 chicks within 2-3 hours at minimal cost.
Jaksch, W. (1981). Euthanasia of day-old male chicks in the poultry industry. International Journal for the Study of Animal Problems, 2(4), 203-213.