Pig Social Behaviour and Welfare: Managing Hierarchies and Aggression

Pigs establish complex social hierarchies and mixing of unfamiliar pigs causes intense aggression that is a major welfare problem in commercial production systems.

Key Facts

Pigs establish social hierarchies through initial fighting when groups are first formed
Mixing of unfamiliar pigs at weaning, post-weaning, and finishing causes severe fighting and injuries
Ear and tail biting can escalate to severe wounds and cannibalism in stressed groups
Stable groups with space allowances sufficient for social avoidance have lower aggression levels
Early socialisation and maintaining stable groups minimises aggression-related welfare problems

Welfare Considerations

Social aggression is one of the most significant welfare problems in commercial pig production. The intense fighting that occurs when unfamiliar pigs are mixed causes severe bite wounds, stress, and sometimes fatal outcomes in individuals who cannot escape attackers in confined spaces. Chronic low-level harassment of subordinate pigs in overcrowded systems causes persistent stress with physiological consequences including immunosuppression. The management practice of repeatedly mixing pigs at different production stages — weaning, grading, moving to finishing — creates repeated episodes of intense fighting. Maintaining stable social groups from weaning to slaughter significantly reduces aggression-related welfare harm and represents a genuine management improvement that is often economically achievable.

What You Can Do

Support pig production systems that maintain stable social groups from weaning to slaughter
Advocate for minimum space allowances that allow social avoidance in pig housing systems
Choose pork from higher welfare certified systems that address mixing and aggression management
Understand the connection between group mixing practices and pig welfare outcomes