Inclusion of grape pomace, in substitution for alfalfa hay, in diets for growing rabbits

Four diets were formulated to study the effect of a progressive substitution of grape pomace (GP) for alfalfa hay (AH) at the rates 0, 100, 200 and 300 g/kg total weight. The control diet contained 500 g AH and 192 g acid-detergent fibre per kg dry matter (DM). In experiment 1, 32 Californian X New Zealand White rabbits were used to determine dietary nutrient apparent digestibility. The inclusion of GP decreased the apparent digestibility of crude protein (P < 0.001) and energy (P < 0.05). However, the digestible energy (DE) contents of the diets were similar because GP had a greater gross energy content than AH. In experiment 2, 3 rabbits given the same diets as in experiment 1 were used to determine several digestive and productive traits and chemical body composition (at 2.0 kg live weight). Dietary inclusion of GP linearly decreased ammonia (P < 0.01), total volatile fatty acid concentration (P < 0.001) and the molar proportion of acetate (P < 0.05) in the caecum. Starch content in the ileal and caecal contents was low but linearly increased (P < 0.05) with increasing dietary concentration of GP. The average daily gain (from weaning at 30 days of age to 2.0 kg live weight) was not significantly affected (P > 0.10) by the diet, but the ratio gain: food linearly decreased (P < 0.001) with the GP inclusion. Dietary inclusion of GP linearly increased (P < 0.10) the fat content of the empty body of the rabbits. The efficiency of utilization of dietary DE and protein for growth were calculated by the comparative slaughter method, using the chemical body composition data of 22 suckling rabbits slaughtered at 30 days of age for the initial body composition. The efficiency of utilization of DE was not influenced by dietary GP inclusion, but GP linearly increased (P < 0.01) digestible crude protein utilization. The decrease in crude protein apparent digestibility may be the main reason that gran: food ratio was impaired in diets containing GP substituted for AH.