Managing Aggression in Pigs: Welfare Through Group Dynamics

Pig aggression at mixing causes serious injuries and chronic stress — understanding and managing social dynamics is essential for welfare-optimized pig production.

Key Facts

• Pigs establish dominance hierarchies through fighting when unfamiliar individuals are mixed
• Mixing injuries include ear tears, flank wounds, and in severe cases, death from sustained attacks
• Mixing stress elevates cortisol for up to 72 hours and suppresses immune function
• Stable groups with familiar individuals show dramatically less aggression than newly mixed pigs
• Management strategies including dim lighting, temporary separation, and familiar-smell introduction reduce mixing aggression

Welfare Considerations

Pig aggression at mixing represents one of the most acute welfare failures in commercial pig production. When unfamiliar pigs are mixed to fill finishing pens, the resulting aggression can be severe — pigs fight intensely for hours as dominance hierarchies are established, with the losers suffering bite wounds to ears, flanks, and tails. Beyond the acute injury welfare harm, the stress of mixing suppresses immunity for days, predisposing to disease. Welfare-optimized management minimizes mixing events by keeping litter groups together from birth through slaughter, uses mixing-reduction strategies when mixing is unavoidable (mixing in neutral spaces, dim lighting, temporary visual barriers), and provides sufficient space for subordinate pigs to escape dominant individuals.

What You Can Do

• Minimize mixing events by keeping litter groups intact from weaning through slaughter where possible
• When mixing is necessary, mix in a new, neutral pen rather than an existing resident pen
• Reduce lighting to near-darkness during the mixing period to reduce visual aggression triggers
• Provide multiple feeding and drinking points to prevent subordinate pigs being excluded
• Monitor new groups hourly for the first 24 hours and separate any pig sustaining serious injury