The effects of ablation of the olfactory bulbs on aggressive behaviour in pigs

Abstract

A dozen young Large White pigs were made anosmic by removal of their olfactory bulbs. Their aggressive behaviour at feeding was observed in groups of two, three and four and also their reaction toward an introduced strange anosmic pig. Control observations were made upon similar groups of pigs which had not been bulbectomized. Olfactory bulb removal did not prevent the formation of dominance relationships but reduced both the level of aggression at feeding (when three or four pigs were present) and that shown towards strangers. Differences in the mean levels of aggression between intact and anosmic animals (expressed as the number of incidents or time spent in aggression) were significant with three ( P < 0.001, P < 0.001) and four ( P < 0.01, P < 0.05) pigs but not with two pigs. The individual introduction of strange pigs (introduced in either a completely immobilised, partially immobilised or normal state) to a normal and a bulbectomized group showed differences in aggressive behaviour and the manner in which the stranger was examined.