Why avoid aggression between pigs?

When unfamiliar pigs are grouped together they fight to establish dominance relationships. This natural behaviour can, under farm conditions, escalate to the extent where health and productivity are affected. Aggression increases stress, causes skin lesions and can result in injury and reduced immunity and growth. Aggression has been researched for several decades but remains undiminished at most farms. Regrouping unfamiliar pigs into a new pen, which causes aggression, is often unavoidable wit