Pig slaughter methods and their welfare implications are a critical but often overlooked area of farm animal welfare, with significant variation in stun effectiveness and the experience of stunning and killing.
The use of high-concentration CO2 for pig stunning creates a documented welfare problem. Pigs are highly sensitive to CO2's aversive properties - the gas causes burning sensation in the airways and extreme distress before unconsciousness. Research using pig behavioral responses and preference tests shows they will endure substantial negative stimuli to avoid CO2 exposure. This means that in the final minute to two minutes of life, billions of pigs annually experience significant aversive suffering before losing consciousness. Lower CO2 concentrations, nitrogen, or argon-based stunning methods cause less distress but are not widely adopted. Improving slaughter welfare for the 1.4 billion pigs killed annually represents an enormous aggregate welfare opportunity.