Pre-slaughter stunning is legally required in most jurisdictions but method effectiveness varies significantly, with welfare implications for billions of birds.
Birds shackled upside down conscious for water bath stunning experience acute stress and pain from the position alone before stunning. Incorrectly calibrated systems may produce tonic immobility rather than unconsciousness. Controlled atmosphere systems, while using a gas with some aversive properties, allow birds to lose consciousness without prior shackling stress. The method choice significantly affects the welfare of billions of birds annually.