There has been much debate on the causes of stereotypy, but the motivational bases of these abnormal behaviours have yet to be fully understood. In the case of oral stereotypies in sows, there is evidence that the motivation to perform feeding behaviour may be involved. Restrictively-fed sows are highly food-motivated for large periods of the day. It has been shown that high-fed gilts perform stereotypies at a lower rate than low-fed gilts indicating that the level of feeding is important (Terlouw et al., 1991). Oral stereotypies in sows occur largely within a specific time after the daily food ration has been consumed. In sows housed in barren pens stereotypy is expressed as excessive drinking or chewing bars or chains, while sows housed on straw will nose and chew the bedding excessively in the same time period after feeding (Burbidge et al, 1993). The behaviour patterns are similar to those used in normal food-searching behaviour, but occur in the absence of reward. It has been suggested that oral stereotypy is the result of the appetitive phase of foraging entering a closed loop of repetition as the normal goal, attainment of more food, cannot be achieved (Hughes & Duncan, 1988). Two experiments were designed to examine the behavioural response to size and frequency of food rewards and they represent the first in a series of experiments which investigate the bases of stereotypies.