Transitions between housing systems, pen groups or environmental conditions are high-welfare-risk periods for pigs requiring careful management to minimise aggression, stress and injury.
Pig housing transition welfare is an acute welfare challenge requiring active management rather than passive observation. The first 72 hours after mixing represent a welfare emergency for some individuals in most groups - severe aggression causes wounds, eye injuries and psychological distress. Management strategies that reduce aggression during transitions (appropriate group size, weight matching, prior olfactory familiarisation, environmental complexity, observation and intervention for severe cases) significantly reduce welfare costs. Farmers who understand that mixing aggression is a management responsibility rather than inevitable pig behaviour make different decisions about transition management. The welfare cost of poor transition management accumulates across every group change in a pig's production life.