Welfare metrics for commercial pig production have evolved from input-based regulations toward outcome-based measures that directly assess animal experience.
The shift from input to outcome measurement represents a fundamental improvement in how pig welfare is assessed and managed. Input standards specify minimum requirements like minimum floor space or maximum stocking density, but animals can experience poor welfare even when all inputs meet standards. Outcome measures assess welfare as experienced by individual animals — whether they are lame, injured, or displaying stress behaviors — regardless of housing specifications. National outcome-based databases allow identification of farm-level risk factors for poor welfare and targeted intervention. The integration of welfare metrics into slaughter audit programs creates a feedback loop between production and welfare outcome that is changing management incentives.