Effect of dietary or abomasal supplementation of exogenous polysaccharide-degrading enzymes on rumen fermentation and nutrient digestibility

The effect of site of supplementation of a mixture of two crude preparation s (Enzyme C and Enzyme X) of exogenous polysaccharide-degrading enzymes (EP DE) was studied in vivo using four ruminally and duodenally cannulated heif ers (Exp. 1). The treatments were as follows: control (no EPDE), EPDE suppl ied through the diet (EF, 47.0 g/d), and EPDE infused continuously into the abomasum (EA, 41.6 g/d). Enzyme treatment increased the concentration of s oluble reducing sugars (P < .05) and decreased NDF content (P < .05) in the treated feed, but this did not increase the rate or extent of in sacco dis appearance of DM from the feed. Compared with control, ruminal fermentation was not affected by EF, but abomasal infusion increased (P < .05) rumen am monia levels and shifted ruminal VFA patterns. Ruminal carboxymethylcellula se (CMCase) and xylanase activities were not affected by treatment. Abomasa l infusion increased (P < .05) duodenal xylanase activity as compared with control and EF, but apparent digestion of DM, NDF, and CP were not affected by treatment. Negligible levels of CMCase and amylase reached the duodenum . During an in vitro experiment (Exp. 2), abomasal stability of the two EPD E was studied over a range of pH from 3.39 to .85, with or without pepsin. Carboxymethylcellulase activity (in Enzymes C and X) and beta-glucanase act ivity (in Enzyme C) were largely unstable against pepsin proteolysis (P < . 001) and low pH (P < .001). Xylanase and amylase activities were resistant to pepsin but irreversibly inactivated at low pH. These two experiments sho wed that abomasal supplementation of EPDE did not successfully supply cellu lases and amylases to the intestine, due partially to their limited resista nce to low pH and pepsin proteolysis. Although EPDE significantly increased the level of xylanase activity at the duodenum, this did not significantly improve total tract digestion.