The majority of UK pigs are stunned before slaughter using carbon dioxide (CO2) gas. CO2 is aversive, causing distress before loss of consciousness, and alternative gas mixtures including argon offer improved welfare outcomes.
Pigs entering CO2 stunning gondolas experience the sharp, burning sensation of high-concentration CO2 for 20-30 seconds before loss of consciousness. This period involves visible distress behaviours including escape attempts, head shaking, and vocalisation. The welfare harm of CO2 stunning is well-documented and could be eliminated by transitioning to argon or nitrogen-based alternatives, but the economic cost of this transition has delayed adoption across the industry.