The use of a second-order schedule to assess the effect of food bulk on the feeding motivation of growing pigs

Abstract

AbstractIt has been suggested that feeding motivation, and hence the incidence of certain abnormal behaviours, may be reduced by the gastro-intestinal distension which results from the ad libitum provision offoods with a high water-holding-capacity (WHO. Therefore, the aim of this experiment was to test the hypothesis that feeding motivation is inversely proportional to the WHC of meals which supply the same level of nutrients. Eight male pigs (initial body weight 54·0 (s.d. 5·76) kg) were offered a series of four foods which possessed increasing WHC due to a linearly increasing inclusion of dried citrus-pulp (2·18, 3·52, 5·60 and 6·92 g water per g dry food for LB, MLB, MHB and HB), but all with similar ratios of digestible energy (DE) to crude protein and minerals. The experimental treatments were allocated in two 4X4 Latin squares with blocks of 6 days separated by a 4-day change-over period. On each day the pigs were given food twice (09.00 h and 16.00 h) to provide the same level of scaled DE across the meals of each treatment. The resulting level offeeding motivation was measured in two successive tests at 30-min intervals before, and eight successive tests at 30-min intervals after, the ingestion of the first meal using a second-order operant conditioning schedule; a methodology which requires pigs to press a paddle to obtain a feeding-related stimuli (CS). It was found that the number ofCS earned pre-feeding was not affected by treatment (17·2, 17·2, 17·6 and 17·5 (s.e.d. 1·58) CS per test for LB, MLB, MHB and HB; P > 0·05), whereas, the number of CS earned post feeding was significantly affected by treatment (16·6, 15·5, 14·6 and 13·8 (s.e.d. 1·15) CS per test for LB, MLB, MHB and HB; P < 0·001). Within each treatment, the number ofCS earned did not alter significantly across any of the time-periods post feeding. As the number of CS earned has been shown to be a reliable indicator of feeding motivation, the results from this experiment support the hypothesis that feeding motivation is inversely proportional to the WHC of iso-energetic meals.