Pig Post-Mixing Aggression: Welfare Management at Group Changes

Mixing of unfamiliar pigs causes severe fighting as social hierarchies are established, with welfare impacts from injuries, stress, and chronic subordinate animal suppression in newly formed groups.

Key Facts

Pigs establish dominance hierarchies through fighting when unfamiliar animals are mixed
Mixing events including weaning, moving to finishing accommodation, and introducing new animals all trigger aggression
Fighting is most intense in the first 24-48 hours but social stress may persist for days to weeks
Injuries including biting, scratching, and occasionally severe wounds occur during and after mixing
Small dark rooms immediately post-mixing, tranquil music, and bedding provision can reduce aggression intensity

Welfare Considerations

Post-mixing aggression in pigs causes acute and significant welfare harm. Fighting causes cuts, abrasions, and in severe cases deep wounds that become infected. The social stress of establishing dominance in an unfamiliar group activates the stress response axis, suppressing immune function and growth. Subordinate pigs in established groups face ongoing welfare compromise from competition for resources and continued aggression from dominant animals. Repeated mixing across the production cycle multiplies welfare incidents. The welfare cost of mixing is well-recognized in pig production science but commercial pressures often override welfare-optimal management of pig social groups.

What You Can Do

Implement stable group management that minimizes unnecessary mixing throughout the production cycle
Use all-in all-out management to reduce the frequency of mixing events
Provide adequate space for subordinate pigs to escape aggressive conspecifics
Use management techniques that reduce post-mixing aggression intensity
Consider wooden boards and additional feeding stations to manage resources in newly mixed groups
Include mixing events and injury rates in farm welfare monitoring and recording systems