Influences of feeding level and physical restriction on development of stereotypies in sows

Abstract

In attempting to understand the mechanisms underlying the development of stereotypic behaviour patterns it is important to determine those environmental factors that contribute to the development of such behaviour. The effects of restraint and food restriction on the development of stereotypies in pregnant nulliparous sows, Sus scrofa, were investigated. In the two housing conditions used in the present study, food restriction, but not restraint, was a major factor in increased levels of activity and in particular high levels of drinking and chain manipulation. Food-restricted sows also increased their feeding rate significantly over the experimental period. Restrained sows spent more time in behaviour such as standing inactive and sham chewing that did not involve manipulation or exploration of substrates. Hughes & Duncan (1988, Anim. Behav., 36, 1696–1707) proposed that stereotypies result from long-term performance of elements of appetitive behaviour. Their model suggests that, in the present study, stereotypies resulted from both environments preventing the animal proceeding to the consummatory phase of foraging behaviour and ‘switching off’ the underlying motivation. This explanation, however, is not consistent with the observation that time spent in appetitive behaviour did not decrease when the level of stereotypy increased, and that stereotypies were concentrated in the post-feeding period. It is also not consistent with the high levels of drinking and chewing of substrates that the food-restricted sows developed, as these activities appear to be more closely related to consummatory behaviour than to appetitive behaviour. It is concluded that there remain a number of aspects of stereotypies in pigs and other species that cannot be wholly explained by current models.