Synergistic Effect of Cellulase and Xylanase on In Vitro Rumen Fermentation and Microbial Population with Rice Straw as Substrate

The in vitro gas test was conducted to investigate the effects of cellulase (CEL) and xylanase (XYL) on in vitro rumen fermentation and microbial population with rice straw as substrate. Three levels of CEL (0, 7.5 and 15 U/g of DM) and XYL (0, 15 and 30 U/g of DM) were tested in a 3×3 factorial arrangement. Addition of CEL and XYL could affect the gas production parameters. Methane emission was increased linearly by CEL addition (P<0.01), while the methane production was greater when XYL added at the intermediate dose (quadratic, P<0.01). Total volatile fatty acids (CEL, quadratic, P<0.01; XYL, linear and quadratic, P<0.05) were enhanced by either CEL or XYL addition. Ammonia nitrogen was reduced by CEL (linear and quadratic, P<0.05), while microbial protein was enhanced by addition of CEL (quadratic, P<0.01) and XYL (linear and quadratic, P<0.01). In vitro degradability of DM and NDF were increased by addition of CEL (quadratic, P<0.05) or XYL (quadratic, P<0.01). Addition of CEL increased the copy number of total bacteria (linear, P<0.01) and Fibrobacter succinogens (linear and quadratic, P<0.05). The outcome of this research indicated that the application of CEL and XYL could improve rumen fermentation, increase rice straw digestion and affect the rumen microbial population. Combination of CEL and XYL at the middle level is more effective than a single CEL or XYL.