Social group composition and stability in pig housing significantly affects aggression, stress, and individual welfare, with mixing of unfamiliar pigs creating acute welfare crises.
Social mixing events represent acute welfare crises in commercial pig production — concentrated periods of intense aggression causing injury, immune suppression, and prolonged stress that affect all individuals involved. The welfare harm is predictable and repeatable: every time unfamiliar pigs are mixed for production reasons (weaning, grading, transport grouping), a welfare cost is incurred. Management strategies that minimize mixing frequency and duration, use pre-mixing familiarization, and provide adequate space and resources during the critical mixing period meaningfully reduce welfare harm. The gold standard — maintaining consistent social groups from birth to slaughter — is achievable in some production systems and eliminates social mixing welfare costs entirely.