Carbon dioxide stunning is the dominant pig stunning method globally but remains controversial because pigs show aversion to CO2, raising serious welfare questions about pre-slaughter experience.
The core welfare problem is the period between exposure and unconsciousness - pigs experience pain, panic and extreme distress. This suffering occurs at massive scale, affecting hundreds of millions of animals annually. Welfare improvements require either modifying CO2 concentration sequences, changing cage descent speed, or transitioning to truly aversion-free alternatives. The economics of slaughter-line throughput currently favour CO2 despite its welfare costs.