The relationship between live weight and the intake of bulky foods in pigs

Data from pigs between 12 and 120 kg live weight were used to develop a relationship between the capacity for food bulk and live weight. High bulk foods, intended to limit growth, were offered for 21 days to pigs of 12, 36 (600 g sugar-beet pulp per kg (SBP₆₀)) and 108 (800 g sugar-beet pulp per kg (SBP₈₀)) kg live weight. Control pigs were given a low bulk food C at all weights. After 21 days the pigs were slaughtered and measurements made on the gastro-intestinal tract (GIT). In two additional treatment groups SBP₆₀ was offered from a weight of either 36 kg or 72 kg before SBP₈₀ was offered at 108 kg. Daily live-weight gain, after allowing for the effects of a change of gut fill, was less at all weights on the high bulk foods than on C. At all weights the high bulk foods caused a significant increase in the weights of the stomach, large intestine, caecum and gut fill. Effects on the weight of the small intestine were small. Previous nutrition had no significant effect on the adapted performance, or on the size of the GIT, of pigs given SBP₈₀ at 108 kg but pre-feeding SBP₆₀ significantly increased initial consumption of SBP₈₀. Constrained intake was not directly proportional to live weight beyond 40 kg. The absolute capacity for bulk (Cap, kg water-holding capacity per day) was related to live weight (W, kg) by the quadratic function Cap = (0.192.W) - (0.000299.W²). The value of Cap is predicted to reach a maximum when W = 321 kg. The combined weights of the large intestine and caecum (WLIC) changed with W in ways that were similar to the way in which Cap changed. In addition the ratio of Cap to WLIC was close to constant. The combined weight of the large intestine and the caecum may determine the capacity for food bulk in pigs.