Pigs are highly social animals that benefit significantly from appropriate group housing, yet commercial pig management practices including mixing of unfamiliar individuals create substantial social stress and aggression problems.
The welfare cost of routine pig mixing is substantial but widely accepted as an operational necessity in commercial production. The aggression that erupts when unfamiliar pigs are combined causes skin wounds, exhaustion, and stress-related immune suppression that makes the pigs more vulnerable to disease in the days following mixing. Stable social groups, by contrast, develop settled hierarchies that require minimal active maintenance and provide social buffering against other stressors. The existence of production systems that maintain stable groups from birth to slaughter demonstrates that mixing is not an inevitable feature of commercial pig farming.