Farm Animals

Pig Welfare: Aggression at Regrouping

Regrouping unfamiliar pigs triggers intense aggression as hierarchies are established, causing significant welfare costs that require management intervention.

Key Facts

Post-regrouping fighting typically lasts 24-48 hours with peak aggression in the first 2-4 hours
Skin lesions from fighting are used as a welfare outcome measure in benchmarking schemes
Temporary darkness, familiarity-promoting bedding, and feeding management reduce regrouping aggression
Boar odour compounds and feed substrate have both shown promise as aggression-reducing interventions at regrouping

Welfare Considerations

Regrouping aggression is one of the most acute welfare challenges in group pig housing. The pain and stress of fighting affects all pigs in a regroup, with subordinate animals experiencing prolonged harassment beyond the initial fighting phase. Management interventions can significantly reduce but rarely eliminate this cost.

What You Can Do

Support pork producers implementing evidence-based regrouping management
Advocate for regrouping aggression to be measured and reported in welfare benchmarking
Engage with research into interventions that reduce regrouping aggression in commercial systems