Farmed Pig Aggression and Social Mixing: A Major Welfare Challenge

Social mixing of unfamiliar pigs triggers intense aggression as animals establish dominance hierarchies, causing injuries and chronic stress that represent one of the most significant welfare challenges in pig farming.

Key Facts

Pigs are highly social animals that form stable hierarchies within familiar groups; introduction of unfamiliar pigs triggers fighting
Mixing occurs at weaning, transfer to rearing accommodation, and entry to finishing units - multiple times per lifetime
Mixing-induced fighting causes skin lesions, ear and tail injuries, and rarely death
The duration of mixing aggression is typically 24-72 hours but can continue at lower intensity for longer
Larger spaces, providing hiding opportunities, and mixing before housing rather than after reduce aggression
Spraying pigs with the same scent before mixing can reduce olfactory recognition of unfamiliar individuals
Ageing individual recognition using visual and chemical cues means aggression is more severe between completely unfamiliar pigs
Short-duration mixing before permanent housing reduces total lifetime fighting compared to multiple mixing events

Welfare Considerations

Mixing aggression in pigs is an unavoidable consequence of management systems that separate and regroup animals multiple times during their lives. The individual welfare cost is real: pigs engaged in sustained fighting suffer pain from bites and injuries, and subordinate animals under repeated attack experience chronic stress. Management strategies that minimise mixing frequency, provide adequate space and visual barriers, and use same-scent treatments are cost-effective welfare improvements. Housing pigs in stable social groups from weaning to slaughter - rarely achieved in commercial practice - would be the most welfare-positive solution.

What You Can Do

Choose pork products from systems that minimise mixing events and provide adequate space
Support research into mixing management strategies that reduce aggression duration and intensity
Advocate for farm assurance standards that set maximum lifetime mixing events for pigs
Donate to farm animal welfare organisations campaigning for improved pig social management
Reduce pork consumption or shift to higher-welfare certified products to reward better management