Contribution of protein, starch, and fat to the apparent ileal digestible energy of corn- and wheat-based broiler diets in response to exogenous xylanase and amylase without or with protease

The ileal energy contribution of protein, starch, and fat in response to 2 exogenous enzyme combinations was studied in 2 digestibility assays with 21- (experiment 1; 432 birds) and 42-d-old (experiment 2; 288 birds) Ross 308 broiler chickens. A 2 × 2 × 3 factorial arrangement of treatments with 2 base grains (corn or wheat), without or with high fiber ingredients (corn distillers dried grains with solubles and canola meal), and 3 enzyme treatments was implemented. Enzyme treatments, fed from 12 to 21 d or 32 to 42 d, were 1) without enzymes, 2) with xylanase from Trichoderma ressei (2,000 U/kg) and amylase from Bacillus licheniformis (200 U/kg; XA), or 3) with XA plus protease from Bacillus subtilis (4,000 U/kg; XAP). All diets contained Escherichia coli phytase (500 FTU/kg). Apparent ileal digestibility (AID) of protein, starch, and fat, as well as the apparent ileal digestible energy, were determined using titanium dioxide as inert marker. A generalized mixed model was used to test main effects and 2-way interactions at P < 0.05. An enzyme × grain interaction was detected for AID of starch at 21 and 42 d, and AID of fat at 21 d, with greater effects of enzymes in wheat-based compared with corn-based diets, but significant increments due to enzymes compared with controls in both diet types. Apparent ileal digestibility of fat at 42 d increased with enzyme supplementation compared with the control treatments. The XA and XAP treatments gradually (P < 0.05) increased AID of protein at 21 d, but only XAP increased AID of protein compared with the control at 42 d. Compared with the controls, XA increased AID energy by 52 or 87 kcal, and XAP by 104 or 152 kcal/kg of DM at 21 or 42 d, respectively. The caloric contribution of starch, fat, and protein were affected differentially by base grain and the presence of fibrous ingredients at 21 and 42 d of age.