Evaluation of the precision-fed rooster assay for detecting effects of exogenous carbohydrases and adaptation diet on true metabolizable energy and cecal microbial ecology, short-chain fatty acid profile, and enzyme activity
Five experiments were conducted to evaluate the precision-fed rooster assay for its ability to detect effects of supplemental carbohydrase enzymes on nitrogen-corrected true metabolizable energy (TMEn) of feed ingredients for poultry. Experiment 1 evaluated six combinations of various α-galactosidase and xylanase levels on TMEn of a corn/soybean meal diet, while Experiment 2 evaluated two levels of a β-glucanase and xylanase on TMEn of pearled barley and rye diets, respectively. Two levels of a multi-carbohydrase combination were also evaluated for both grains. In both experiments, Single Comb White Leghorn roosters were fasted for 26 h and then crop intubated with either 25 or 30 g of the test diets. Excreta were collected quantitatively for 48 h after feeding. In Experiment 1, all carbohydrase combinations either numerically or significantly (P < 0.05) increased TMEn of the corn/soybean meal diet and the mean increase for the enzyme treatments was 66 kcal/kg DM compared with the control diet containing no added enzymes. In Experiment 2, both β-glucanase and the multi-carbohydrase combination significantly (P < 0.05) increased TMEn of the 100% barley diet, while the xylanase and multi-carbohydrase combination either numerically or significantly (P < 0.05) increased TMEn of the 100% rye diet. Overall, results of Experiments 1 and 2 indicated that the precision-fed rooster assay can detect effects of carbohydrase enzymes on TMEn of diets containing corn/soybean meal, pearled barley, and/or rye. Experiments 3-5 evaluated the hypothesis that TMEn of barley and rye diets may be influenced by type of pre-trial adaptation diet and exogenous carbohydrases. Single Comb White Leghorn roosters were fed adaptation diets based on corn/soybean meal, barley/soybean meal with and without β-glucanase, and/or rye/corn/soybean meal with and without xylanase for approximately 4 wk. After the adaptation period for Experiments 3 and 4, TMEn was determined for 100% barley or 100% rye diets with or without β-glucanase or xylanase, respectively. Cecal samples were also collected either at the end of the 4 wk adaptation period or at the end of the TMEn assay for analysis of microbial ecology, short-chain fatty acid (SCFA) profiles, and β-glucanase and xylanase activity. β-Glucanase significantly increased (P < 0.05) the TMEn of barley and xylanase numerically increased the TMEn of rye, but there was no significant effect of adaptation diet on TMEn values. Total Eubacteria and Ruminococcaceae were decreased (P < 0.05) but Escherichia coli was increased (P < 0.05) at the end of the TMEn assay compared with the values obtained at the end of the adaptation period (with no TMEn assay), and there was a large decrease (P < 0.05) for most SCFA at the end of the TMEn assay compared with the end of the adaptation period. For cecal enzyme activity, both β-glucanase and xylanase activity were increased for adaptation diets containing the respective enzyme. In Experiment 5, which only included feeding the adaptation diets for 4 wk, there were no consistent effects of adaptation diet on cecal microbial profiles and SCFA but again, both β-glucanase and xylanase activity were increased (P < 0.05) for adaptation diets containing the respective enzyme. Overall, the results of this study indicated that the precision-fed rooster assay is sensitive for detecting the effects of exogenous β-glucanase on TMEn of barley and the effects of exogenous xylanase on TMEn of rye. Adaptation diet did not significantly influence the TMEn response to the exogenous enzymes, possibly because cecal fermentation (based on SCFA) was greatly reduced by the extensive fasting during the TMEn assay. Cecal β-glucanase and xylanase activity were often increased by feeding high barley and high rye diets with inclusion of exogenous enzymes.
Carbohydrase, β-glucanase, xylanase, barley, rye, enzyme.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign