Pig Social Hierarchy and Mixing Stress: Welfare During Group Formation

Mixing unfamiliar pigs causes intense aggression and injury, making social management one of the key welfare challenges in pig farming.

Key Facts

Pigs establish dominance hierarchies through physical contests when unfamiliar individuals meet
Mixing events occur repeatedly in commercial production — at weaning, after nursery, and into finishing groups
Mixing injuries include skin lacerations, ear damage, and occasionally serious trauma
Stress from mixing suppresses immune function and impairs growth for days after events
Larger groups mixed in larger spaces show reduced injury compared to small groups in confined spaces
Pen design with visual barriers and escape routes can reduce injury severity during mixing

Welfare Considerations

Social mixing is one of the most acute welfare events in the life of a commercial pig. The aggression that occurs when unfamiliar pigs meet is genuine fighting — not play — and results in real injury and significant physiological stress. Welfare-positive management minimises the number of mixing events across a pig's life, uses pen design that allows escape from aggression, provides visual barriers that limit continuous eye contact, and applies mixing during lower-risk periods such as after feeding. Some producers use pheromone sprays to reduce aggression at mixing, with mixed but sometimes significant welfare benefit. Research into stable group management from weaning to slaughter is a priority welfare improvement area.

What You Can Do

Support pork from farms that minimise mixing events through stable group management
Advocate for pen design standards that reduce mixing injury through appropriate space and barriers
Engage food companies about their standards for social management in pig supply chains
Support research into pheromone and management interventions that reduce mixing stress
Choose higher-welfare pork labels that specify social management standards