Ingestion of food facilitates the performance of stereotypies in sows

Previous work has shown that chain manipulation and excessive drinking develop in sows, Sus scrofa, only when the sows are food restricted and confined, and that their occurrence is concentrated mainly in the post-feeding period. The present study investigated whether ingestion of food stimulates the performance of these stereotypies. In experiment 1, sows had been exposed to 7 months of restrictive housing and feeding conditions (2.5 kg of food/day; normal feeding time 0900 hours), during which they had developed stereotypies, mainly stereotyped chain manipulation and excessive drinking. Treatments, applied at 1350 hours, were the introduction of a novel sound (duration 10 min) and delivery of an extra meal (ingestion time approximately 10 min). Each treatment was applied to all sows simultaneously on two separate occasions. Levels of stereotypies measured over 2 h after the novel sound did not differ from preceding control days. In contrast, levels of stereotypies measured over the 2 h following ingestion of the meals were significantly higher relative to controls. In experiment 2, subjects were sows normally fed a meal of 2.5 kg of concentrated food at 0900 hours, which had already developed chain manipulation and excessive drinking. On treatment days, at 0900 hours, they received 0, 0.5, 1.25 or 5 kg of the same food. Non-delivery of food was followed by reduced levels of both chain manipulation and drinking. Ingestion of a smaller or larger meal than usual had little effect on levels of post-feeding stereotypies. The results of both experiments suggest that ingestion of food stimulates the performance of established stereotypies. The effect cannot be explained simply by differences in nutritional status, and it is suggested that it reflects changes in motivational state and behavioural activation.