THE EFFECT OF FAT INCLUSION ON DIET DIGESTIBILITY IN GROWING RABBITS

Fifty-six California x New Zealand rabbits were used to study the infl uence of fat addition on nutrient digestibility. Seven diets were form ulated 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, respective ly; 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 et her extract (EE) by 3%. After the digestibility trial, rabbits (weighi ng 2.00 +/- .13 kg) were slaughtered to determine the composition of c ecal contents. Fat addition increased digestibility of energy (P < .05 ) and EE (P < .001). The type of fat only affected (P < .05) EE digest ibility. No interaction between fat types and WS was found. Although E E levels of cecal contents increased in diets with added fat (P < .001 ), they did not negatively affect dietary fiber digestibility. The pat terns 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 incre ases as its degree of unsaturation increases. Digestibilities of C16:0 and C18:2 were, respectively, lower and higher in the diet with 3% so ybean 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 t he 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 t he digestibility coefficients measured were higher in young than in ad ult rabbits.