Pre-slaughter stunning is legally required for pigs in the EU and UK, but the humaneness of different stunning methods varies significantly and remains an area of active welfare research.
Pig slaughter stunning welfare is a case where legally compliant practice may still cause significant suffering. CO2 stunning meets the legal requirement of causing loss of consciousness before slaughter, but the pathway to that insensibility involves acute respiratory distress as high CO2 concentration triggers carbon dioxide receptor activation. The 15-30 seconds of consciousness in high CO2 represents genuine suffering for each individual pig. Alternative inert gas mixtures (argon/nitrogen) avoid this aversive pathway, producing unconsciousness without the sensory alarm response. The welfare case for transitioning away from CO2 is strong based on available evidence. Economic barriers are real but not insurmountable, particularly for larger integrated slaughter operations.