Group size significantly affects pig welfare through its influence on social stability, aggression, resource access, and the ability of pigs to establish and maintain dominance relationships.
Group social dynamics profoundly affect pig welfare. Pigs establish linear dominance hierarchies that reduce ongoing aggression in stable groups, but frequent remixing — common in commercial systems — repeatedly disrupts these hierarchies, causing fighting and injury. Very large groups exceed the cognitive capacity of pigs to track social relationships, leading to increased anxiety and aggression. Stable, smaller groups with adequate space and enrichment allow more normal social behaviour. When group mixing is unavoidable, provision of hiding areas and increased space reduces the welfare costs of social disruption.