Pig social groups have stable hierarchies established through fighting — the welfare cost of repeatedly mixing unfamiliar pigs is one of the most significant and preventable harms in pig farming.
The cycle of mixing unfamiliar pigs — at weaning, in transport, at auction, in finishing groups — inflicts repeated rounds of fighting and injury on animals who, if left in stable groups, would live with far lower levels of conflict. Each mixing event triggers a social crisis that causes measurable suffering, reduced growth and physical injury. Minimal mixing strategies that maintain social stability from birth to slaughter are feasible in commercial pig production and represent one of the most impactful single management changes available. The welfare case is reinforced by the production case: stable groups grow faster and have lower injury rates than repeatedly mixed pigs.