Interactions between dietary fat type and enzyme supplementation in broiler diets with high pentosan contents: effects on precaecal and total tract digestibility of fatty acids, metabolizability of gross energy, digesta viscosity and weights of small intestine

One hundred grams fat, based on blends of beef tallow and soya oil (0:100, 20:80, 40:60, 60:40, 80:20 and 100:0) which corresponded to dietary ratios of unsaturated to saturated fatty acids (U:S ratio) of 5.47, 3.23, 2.11, 1.45, 1.00 and 0.69, respectively, was incorporated into a rye-based broiler diet (610 g kgÿ1). All diets were tested without or with supplementation of a xylanase-containing enzyme preparation in a combined growth test and balance study. Increasing the proportion of dietary tallow resulted in depression in live-weight gain and increased feed conversion ratio, exponential increase in jejunal supernatant viscosity, increased empty weight of small intestine and reduced digestibility of fat and fatty acids and metabolizability of gross energy. The bene®cial effect of addition of xylanase was greatest at higher tallow concentrations. In diets which were not supplemented with enzyme, it was shown that small incremental increases in U:S ratio up to 1.5 resulted in distinct incremental increases in digestibility, whereas ratios exceeding this value had virtually no further bene®t. Such effects were less pronounced in enzyme supplemented groups. Animal Feed Science and Technology