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.(ABSTRACT TRUNCATED AT 250 WORDS)