Nutrient and fiber utilization responses of supplemental xylanase in broiler chickens fed wheat based diets are independent of the adaptation period to test diets.

The effects of adaptation (AD) to xylanase-supplemented diets on nutrient and fiber utilization in 21-d-old broilers were investigated. Six treatments, arranged in two levels of AD (starting at d 0 or d 14 of age) and three levels of xylanase (0 or 2,500 or 5,000 xylanase units/kg feed) were used. All diets had 500 phytase U/kg and 0.3% TiO2 as indigestible marker. A total of 384 d old male broiler (Ross 308) chicks were divided into two groups. The first group was assigned on weight basis to 24 cages (8 chicks per cage) and randomly allocated to the diets from d 0. Birds in the second group were reared on a commercial starter diet in the same room for 13 d. On d 14, the birds were individually weighed, assigned on weight basis to 24 cages (8 chicks per cage), and randomly allocated to the diets. Birds had free access to experimental diets and water. Excreta samples were collected from d 18 to 21. On d 21, all birds were euthanized to access ileal digesta. There was no interaction (P > 0.05) between AD and xylanase on the apparent ileal digestibility (AID) and apparent retention (AR) of components. The main effect of AD was such that the birds exposed to diets for 7 d (d 14 to 21) had higher (P < 0.01) AID of energy than those exposed for 21 d (d 0 to 21). In contrast, birds exposed to diets for 21 d had higher (P < 0.05) AMEn and AR of neutral detergent fiber. Xylanase improvements (P < 0.01) in the AID of energy and AMEn were dose dependent and coincided with linear improvements (P < 0.05) in the AID of nitrogen, fat, and starch. In conclusion, xylanase improvements on retention of fiber and nutrients were independent of AD (7 or 21 d) suggesting that the xylanase effects are not transitional. Greater retention of fiber with longer AD is suggestive of possible microbial adaptation.