A review of the factors influencing the aggressive and agonistic behaviour of the domestic pig

The literature describing aggressive and agonistic interactions between domestic pigs is reviewed. This is followed by a review of the effects of fighting in pigs and the environmental factors which affect levels of aggression in groups of pigs. We conclude that the mixing of unacquainted pigs should be kept to a minimum as this results in high levels of aggression, leading to physical injury and physiological changes. There have been contradictory results from mixing evenly and unevenly weighted pigs. The size of the mixed groups seems to have little effect on levels of agression; however, in the studies that have been carried out, group sizes have not been very different. Tranquillisers appear to be effective in reducing aggression, but they would be expensive to use on a regular basis. The pheromone 5a-androst- 16-en-3-one reduces aggression and acts as a growth promotant, but it has only been used experimentally. Competition for feed and space leads to increased aggression, but the provision of barriers between feeding animals and secure areas, into which pigs can escape, appear to reduce aggression. It is suggested that further work should be carried out into pen design as this seems to be a simple method of reducing aggression between animals.