Studies On The Relationship Between Xylanase Supplementation And Total Xylans Content In Broiler Diets

The TME assay was used to investigate the effect of dietary xylan content andsupplementation of xylanase on the nutrient utilization and to establish the quantitative relationship between xylanase supplementation and dietary xylan content in broiler diets. Five basal diets with five levels of xylans were designed .The level of xylans was adjusted by the wheat and wheat bran in the proportion of 3:1 to replace corn. Five TME assay trials were conducted to determine the nutrient utilizations of the five diets in different xylan contents. For each assay trial, there were 7 treatments, 6 of which were 6 levels of xylanase supplementation and 1 of which was designed to determine the endogenous nutrient excretion by starvation. 56 healthy adult Avian broilers were allocated randomly to 7 treatments with 8 replicates of 1 bird per replicate in each trial. The birds were force-fed with the diet at the amount of 2% of body weight after 48-hr starvation. Excreta was then collected for 48hrs. The results are as follows:1. With the increase of the xylan contents in broiler diets , the true availabilities of nutrients except P decreased. When dietary xylan content increased from 4.13% to 7.43%, the true availabilities of dry matter (DM ) , crude protein (CP ) - calcium ( Ca) and energy were decreased by 9.66% (P<0.01) , 14.58% (P > 0. 05) , 27.25% (P<0.10) , 10.81% (P<0.01) respectively. Regression analysis showed that there were highly negative linear relationships between DM, CP and energy availabilities and dietary xylan contents . When dietary xylan content increased 1 percentage , the true availabilities of DM, CP and energy decreased by 1.84, 3.12, 2.09 percentage respectively.2. Xylanase supplementation improved one availiabilities of nutrients in the corn-soybean meal based diets to a certain extent. The supplementation of 225u xylanase per kg diet enhanced significantly the true availabilitity of DM and the TME and TMEn values by 5.23%, 4.51%, 4.33% respectively in the corn-soybean meal based diet containing 4.13%xylans.3. The optimum supplementation of xylanase was 900u/kg diet for the diet containing7.432% xylans. TME and TMEn were improved by 8.03% (P<0.01) and 7.52% (P<0.01) , and true availabilities of DM and CP, by 8.99 % (P<0.01) and 42.41 % (P<0.01) respectively at this xylanase supplementation level. The improvements of nutrient availabilities were not significant for the diets containing 4.50%.The results show that dietary xylan content and xylanase supplementaion levels are 'quantitatively related with nutrient availabilities for broilers. In this experiment , the true availiabilities of DM and energy are significantly decreased when xylan content reaches 6.39%, and those of DM,CP and energy are highly significantly decreased when xyan content grows to 7.43%. The improvement of nutrient availiabilities is not significant after xylanase is added into diets until the dietary xylan content is high enough.