Mixing Aggression and Pig Welfare After Introduction

Introducing unfamiliar pigs to established groups causes intense fighting that is one of the most significant acute welfare events in pig production.

Key Facts

Pigs establish dominance hierarchies through fighting — mixing unfamiliar pigs causes an acute aggression peak lasting 24-72 hours
Injuries from mixing fights include lacerations, haematomas, eye damage and, in extreme cases, death from exhaustion or blood loss
Pigs have better long-term welfare in stable social groups — repeated mixing disrupts social structure and causes chronic stress
Mixing at feeding time or in barren environments without escape routes dramatically worsens aggression severity

Welfare Considerations

Mixing aggression imposes one of the most concentrated acute welfare costs in pig production. A single mixing event can generate dozens of fights in the first hour, leaving multiple animals with significant injuries. The welfare impact is compounded by the fact that subordinate individuals cannot escape in confined pen environments. Mitigation strategies including mixing during feeding, providing straw enrichment, using dark pens for initial mixing and including escape barriers reduce but do not eliminate aggression-related welfare costs. Avoidance of unnecessary mixing is the primary welfare intervention.

What You Can Do

Minimise pig mixing events throughout the production cycle — plan group sizes to avoid remixing at key stages
Provide deep straw bedding at mixing to redirect aggression toward substrate investigation
Mix pigs in the evening in darkened conditions to reduce initial aggression intensity
Ensure all pens have escape routes and refuges where subordinate animals can avoid dominant conspecifics