How poultry are rendered unconscious before slaughter varies significantly across the industry. The method used has profound welfare implications for billions of birds each year.
Slaughter welfare for poultry involves welfare concerns at multiple stages: shackling while conscious (which causes pain and stress), the stunning process itself, and the interval between stunning and neck-cutting. Water bath stunning has documented failure rates causing some birds to enter scalding tanks conscious. The inversion required for shackling causes distress and may cause pain through wing joint pressure. Controlled atmosphere systems avoid shackling-while-conscious but the gas mixture and concentration significantly affect the aversiveness of the induction process. Multi-phase CAS with an initial inert gas phase avoids aversive CO2 and is the highest-welfare available option for large-scale poultry slaughter.