THE EFFECT OF FAT INCLUSION ON DIET DIGESTIBILITY IN GROWING RABBITS

Fifty-six California x New Zealand rabbits were used to study the influence of fat addition on nutrient digestibility. Seven diets were formulated to a 24% ADF level: Diet C had no added fat; Diets T, O, and S contained 3% of added beef tallow, oleins, and soybean oil, respectively; and Diets TWS, OWS, and SWS contained the same level and types of fat but also 18% heated whole soybean meal (WS) to increase dietary ether extract (EE) by 3%. After the digestibility trial, rabbits (weighing 2.00 +/- .13 kg) were slaughtered to determine the composition of cecal contents. Fat addition increased digestibility of energy (P < .05) and EE (P < .001). The type of fat only affected (P < .05) EE digestibility. No interaction between fat types and WS was found. Although EE levels of cecal contents increased in diets with added fat (P < .001), they did not negatively affect dietary fiber digestibility. The patterns of fatty acid digestibility in Diet C and in those with soybean oil (S and SWS) were similar; the lowest values were obtained for C16:0 and C18:0. The digestibility of unsaturated fatty acids of C18 increases as its degree of unsaturation increases. Digestibilities of C16:0 and C18:2 were, respectively, lower and higher in the diet with 3% soybean oil than in the diet with 3% tallow. In a second trial, 36, 31-d-old rabbits (weaned after milk meal on d 29) were used to determine the nutrient digestibility of Diets C, T, S, and SWS. Fat addition did not affect digestibility coefficients of young rabbits except for that of EE, which increased (P < .001) with the level of dietary EE. All the digestibility coefficients measured were higher in young than in adult rabbits.