The effects of supplying increasing ruminal doses of exogenous polysaccharide-degrading enzymes (EPDE) on rumen fermentation and nutrient digestion were studied using eight ruminally cannulated heifers, four of which were also duodenally cannulated, in a replicated Latin square. The heifers were fed a diet of 85.5% rolled barley grain and 14% barley silage (DM basis), and once daily they were given intra-ruminal doses of O (Control), 100, 200, or 400 g of a preparation containing polysaccharide-degrading enzymes. Enzyme treatment decreased ruminal pH (linear, P < .001) and increased ammonia N (quadratic, P < .001) concentration. The ruminally soluble fraction and effective degradability of feed DM in situ were increased (quadratic response, P < .001) by enzyme treatment. Ruminal administration of EPDE increased ruminal fluid carboxymethylcellulase and xylanase activities linearly (P < .001) and β-glucanase activity quadratically (P < .01), decreased (quadratic response, P < .05) ruminal fluid viscosity, and did not affect (P > .05) ruminal fluid amylase activity. Elevated levels of fibrolytic activities in the rumen resulted in increased (quadratic, P < .001) carboxymethylcellulase, xylanase, and β-glucanase (P < .01) activities in duodenal digesta. Duodenal amylase activity and reducing sugar concentration were also increased (quadratic responses, P < .001 and P < .05, respectively) by EPDE. Xylanase activity of fecal DM was increased linearly (P < .05) with increasing ruminal EPDE levels. Apparent digestibilities of DM, crude protein, and NDF were not affected by EPDE supplementation. Enzyme treatment did not affect (P > .05) urinary excretion of allantoin and uric acid, or concentrations of glucose and urea in blood.
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