Carbon dioxide stunning is the dominant pig slaughter method globally but is aversive and causes distress before insensibility; alternatives are available but not widely adopted.
CO2 pig stunning presents one of the most significant known welfare harms in commercial slaughter that is not yet adequately addressed by regulation. Pigs entering the high-CO2 chamber show clear aversive responses — head shaking, gasping, retreating — for up to 30 seconds before losing consciousness. This distress period is equivalent to asphyxiation and represents significant suffering for tens of millions of animals per year in the EU alone. Inert gas stunning using nitrogen or argon mixtures renders pigs unconscious without the aversive phase but costs more to implement. The welfare case for transition is strong; the barrier is industry investment cost.