THE EFFECT OF FOOD-DEPRIVATION ON THE EXPRESSION OF FORAGING AND EXPLORATORY-BEHAVIOR IN THE GROWING PIG

Growing pigs spend considerable time orally manipulating their environment including straw and their pen-mates, leading to problems such as tail biting. It is unclear if this active behaviour reflects either foraging motivation, exploratory motivation or a combination of both. This problem is exacerbated by the possibility that both motivational systems share certain behavioural elements. The aim of this experiment was to determine the extent to which appetitive foraging is separable from intrinsic exploration by manipulating both feeding motivation and the novelty of the external environment. The behaviour of 12 growing male pigs was recorded during tests lasting 35 min whilst placed in a familiar test arena with a woodbark/sand foraging substrate. Tests were conducted in blocks lasting 8 days during which pigs were fed a commercial food either ad libitum (Treatment H) or at a 20% reduction thereof (Treatment L). A replicated Latin square design allowed pigs to be twice provided with either novel objects, food (50 g) or nothing in a specific 'target-area' of substrate at either feeding level. Food restriction although not affecting locomotion resulted in an increase in the proportion of time spent rooting the substrate (0.05 vs. 0.08 for H versus L pigs respectively; standard error of the difference (SED) 0.008; P<0.01), a decrease in the proportion of time spent lying (0.17 vs. 0.12; SED 0.027; P<0.05), and an increase in the proportion of time spent in the target-area (0.05 vs. 0.08; SED 0.011; P< 0.05), with no effect of novel object presentation in any case. The presentation of novel objects resulted in an increase in the rate of visits to the target-area (0.30, 0.23 and 0.24 for novel objects, food and control treatments respectively; SED 0.025 visits min(-1); P<0.05) which was independent of feeding level. These results indicate that the increase in rooting and decrease in lying is a reflection of an increased level of feeding motivation produced by food restriction. Rooting was an expression of appetitive foraging as it was unaffected by never object presentation. The increase in frequency of visits to the target-area due to novel object presentation was an expression of intrinsic exploration as it was independent of feeding motivation. Therefore, it was concluded that appetitive foraging behaviour and intrinsic exploration can be experimentally separated by the controlled manipulation of both feeding motivation and specific environmental stimuli.