Group size affects social dynamics and aggression. Large groups (>20 pigs) can dilute aggression from unfamiliar pigs by making individual recognition impossible. Small, stable groups allow hierarchy establishment with less chronic aggression. Research shows optimal group sizes of 10-20 for welfare outcomes in most commercial contexts.
EU minimum space for finishing pigs (0.65-1.0 m² per pig depending on weight) is insufficient to meet behavioral needs according to welfare science. Studies consistently show reduced aggression, better activity budgets, and lower cortisol at 20-30% above minimum allowances. Higher-welfare certification schemes typically specify higher space allowances.
Mixing pigs from different litters or pens creates severe aggression as hierarchies are re-established. Mixing should be minimized after weaning wherever possible. When unavoidable, strategic mixing (at feeding time, in novel environments, under darkness) reduces aggression severity. Post-mixing monitoring for injuries is essential.
The EU directive requires pigs to have constant access to enrichment materials. Straw, wood, and manipulable objects maintain engagement and reduce redirected aggression. Enrichment must be renewed regularly to maintain novelty. Slotted floor systems require design modifications to accommodate straw or other substrate enrichment.
Tail biting in finishing pigs is both a welfare harm (victim suffering) and an indicator of pen-level welfare failure (sub-optimal conditions). Prevention integrates enrichment, space, ventilation, nutrition, and health management. Early detection of tail biting (regular inspection, bite wound monitoring) enables rapid intervention before escalation.
Terminal cross breeds (Pietrain × commercial lines) are selected for fast growth and lean meat deposition. Some trait combinations create welfare trade-offs: high lean growth is associated with stress susceptibility (PSS — porcine stress syndrome). Breed selection that avoids welfare-compromising traits is part of a systems approach to finishing pig welfare.