Pig Aggression When Mixing Groups

Mixing unfamiliar pigs causes intense aggression as animals establish dominance hierarchies. Welfare-informed management strategies can substantially reduce injury and suffering.

Key Facts

Pigs establish linear dominance hierarchies through fighting, which can last 24-72 hours after mixing
Injuries from mixing include lacerations, eye damage, ear tears, and vulva biting
Commercial systems routinely mix pigs at weaning, after gestation, and at finishing barn entry
Larger group sizes (40+ pigs) paradoxically reduce injury rates compared to small groups
Providing ample space (>0.75 m2 per pig) and visual barriers reduces confrontation severity
Pigs recognize individual pen mates and do not re-establish hierarchy with familiar animals

Welfare Considerations

Mixing aggression causes acute pain, injury, and psychological stress for millions of pigs globally each year. Animals sustaining serious wounds suffer chronically if not treated. Welfare-positive mixing strategies include mixing at night (lower activity), providing additional space at mixing, using visual barriers (hanging chains, partitions), applying odor masking to reduce olfactory recognition of strangers, and progressively familiarizing groups before full contact. Eliminating unnecessary mixing events (e.g., keeping litters together from birth to slaughter) is the most effective welfare intervention.

What You Can Do

Support pork supply chains that minimize group mixing events throughout the production cycle
Advocate for space allowance standards that reduce confrontation severity after mixing
Choose pork certified under standards requiring appropriate space and mixing protocols
Support research into pheromone products and other interventions that reduce mixing aggression