Pigs exhibit a range of abnormal behaviours (e.g. stereotypies or tail-biting) which may, at least in part, be linked to feeding regimes which produce high levels of feeding motivation. Therefore, a welfare dilemma exists because the quantitative food restriction of sows and boars remains an essential husbandry practice to reduce excessive weight-gain and maintain breeding efficiency. However, it has recently been proposed that underlying levels of feeding motivation may be reduced through the ingestion of foods of high bulk (e.g. Brouns et al .,1994). These foods may serve to reduce feeding motivation through gastro-intestinal distension rather than by increased nutrient supply. Therefore, the aim of this experiment was to investigate whether iso-energetic foods with different bulk characteristics (water-holding-capacity - WHC) affect the level of feeding motivation, and if so, the duration of their effect.