Pigs are intensely social animals with complex dominance hierarchies. Their social structure in commercial systems — frequently disrupted by regrouping — creates some of the most significant welfare challenges in pig production. Understanding pig social behavior is essential for welfare-positive management.
Pigs in stable groups maintain clear dominance hierarchies established through fighting and maintained through submission signals. In stable groups, agonistic encounters are brief and low-level — subordinate pigs signal submission and dominant pigs rarely need to escalate. The welfare of stable group pigs is significantly better than that of frequently mixed groups, because chronic stress from social instability is avoided.
The welfare case for stable social groups: pigs in stable groups show lower cortisol baselines; fewer wounds; more play behavior; better growth rates; and reduced medication use. The management implication: minimize regrouping events; keep litter groups together from birth to slaughter where possible; avoid mixing pigs from different farm sources; and provide sufficient resources (feeders, space) to reduce competition-related aggression.
Commercial pig production frequently requires regrouping: at weaning, at move to growing facilities, at introduction to new pens, and during grading. Each mixing event causes: 24-72 hours of elevated fighting; wounds to ears, flanks, and tails; cortisol spikes; reduced feeding (subordinate pigs unable to access feeders); and occasional severe injuries requiring veterinary treatment. Mixing is the single most predictable acute welfare event in pig production.
In resource-limited environments, dominance hierarchy effects are amplified. Too few feeder spaces, water points, or lying areas create competition that disadvantages subordinate animals: they eat less, rest less, and experience chronic stress from repeated challenges. Welfare guidelines recommend minimum feeder and water access ratios; ad libitum feeding eliminates feed-access competition.