The method used to stun pigs before slaughter is one of the most welfare-significant decisions in pig production. Carbon dioxide stunning - the dominant commercial method - causes distress before loss of consciousness.
CO2 stunning creates a significant welfare problem that is known, documented, and ongoing across the European pig industry. Research consistently shows that pigs placed in high-concentration CO2 experience aversion - they try to escape, rear up, vocalize, and show signs of respiratory distress before losing consciousness. The 20-30 seconds of aversion before unconsciousness may seem brief, but for the billions of pigs passing through this system annually, the cumulative welfare cost is enormous. The existence of inert gas alternatives that cause unconsciousness without aversion makes CO2 stunning's persistence largely an economic choice - CO2 systems are cheaper and operationally simpler than alternatives. Welfare advocates have made CO2 stunning a major campaign target, with some success in major retailers requiring suppliers to transition.