Carbon dioxide stunning is widely used for pigs despite evidence that pigs find high CO2 concentrations highly aversive. Alternative stunning methods are available and increasingly adopted.
CO2 stunning welfare presents a clear case where evidence of animal aversion should drive industry change but has not. The evidence that pigs find high CO2 concentrations highly aversive - exhibiting frantic escape attempts, distress vocalizations, and head shaking - is scientifically robust. The pre-unconsciousness period of 20-30 seconds represents significant suffering at enormous scale given the billions of pigs stunned annually. Inert gas alternatives using argon or nitrogen eliminate this aversive period, maintaining the practical advantages of group stunning. The transition cost for existing systems is the primary barrier - a cost that should be weighed against the aggregate suffering of current methods.