The size of pig social groups affects welfare outcomes through its influence on aggression, disease dynamics and stress.
Group size influences pig welfare in complex ways. Very small groups can lead to intense social pressure in barren environments. Very large groups prevent the formation of stable social hierarchies leading to chronic instability. Medium-sized stable groups with adequate resources and enrichment represent the welfare optimum in most commercial settings. Space, resources and enrichment matter as much as group size in determining welfare outcomes.