The method of stunning and slaughter used for pigs significantly affects welfare at the end of life, with carbon dioxide stunning — the most common method — causing aversion and distress before inducing insensibility.
Carbon dioxide stunning imposes a period of conscious distress on every commercially stunned pig — an estimated 100+ million animals annually in the US alone. The experience before insensibility involves a burning sensation in the airways and panic-level fear responses. While this distress is brief compared to a life of poor welfare in intensive housing, it represents a significant and largely avoidable welfare cost at the moment of death. Low-atmosphere argon systems cause less distress but are more expensive to implement. The welfare science on CO2 is clear and has been for decades — the continued widespread use reflects economic rather than welfare-based decision making.