Influence of direct-fed exogenous fibrolytic enzyme on ruminal fibrolityc activity in sheep

Abstract

Six rumen-fistulated Merino sheep were used in a crossover design experiment to evaluate the effects of a direct-fed exogenous fibrolytic enzyme (12 g/d; ENZ) on ruminal fermentation. The enzyme presented endoglucanase and xylanase activities. Sheep were fed a mixed grass hay:concentrate (70:30; fresh matter basis) diet at a daily rate of 60 g/kg body weight 0.75. Concentrations of NH3-N and volatile fatty acids (VFA) and enzymatic activities were determined in ruminal samples at 0, 4 and 8 h after feeding. Samples of the grass hay were incubated in situ in the rumen of each sheep to measure dry matter (DM) and neutral detergent fibre (NDF) degradation. ENZ treatment did not affect (P>0.05) ruminal pH or concentrations of NH3-N and total VFA at any sampling time. In contrast, at 0 and 4 h after feeding, molar proportion of propionate tended (P<0.10) to be greater and acetate:propionate ratio tended (P<0.10) to be lower in ENZ-supplemented sheep. No effects of ENZ (P>0.10) were detected 8 h after feeding. Both the ruminally insoluble potentially degradable fraction (b) of grass hay DM and its fractional rate of degradation (c) were increased (P<0.05) by ENZ treatment. Supplementation with ENZ also increased (P=0.009 to 0.023) effective and potential degradability of grass hay DM and NDF. Ruminal fluid endoglucanase and xylanase activities were greater (P<0.05) at 4 h post-feeding in ENZ-supplementd sheep than in control animals. ENZ supplementation did not affecf (P=0.151 to 0,815) either exoglucanase or amylase activity at any sampling time.