Controlled atmosphere stunning (CAS) is increasingly recognised as the most humane method for rendering poultry unconscious before slaughter, avoiding the welfare problems of live-shackle systems.
The welfare problems of conventional live-shackle electrical stunning are substantial. Birds are hung upside down while fully conscious, experiencing inversion stress and physical pain. Electrical stunning failures mean a significant proportion of birds reach the neck-cutter while still conscious. Controlled atmosphere stunning avoids all these problems: birds remain in their transport crates and lose consciousness gradually through gas inhalation without prior handling stress. High-concentration CO2 causes some discomfort before unconsciousness, making low-oxygen or CO2/inert gas mixtures preferable welfare options. Converting the poultry industry to CAS would represent one of the largest single welfare improvements achievable for farm animals given the enormous numbers affected.