255 Determining the optimal dose of microbial enzyme to enhance fiber digestion

Abstract

Abstract Certain enzymes may enhance fiber digestion, but the optimum dosage for ruminants consuming bermudagrass hay is not known. The objective of this study was to determine the optimal dosage of a combination of a protease with Aspergillus oryzae and A. niger fermentation extract blend on fiber digestion and rumen fermentation of bermudagrass hay by sheep. Twenty ewes (30.3 ± 5.29 kg BW) were allocated randomly to 1 of 5 diets (n = 4/treatment). Bermudagrass hay was chopped and offered for ad libitum consumption to ewes housed individually in 1 × 1.5-m pens with plastic-coated grate flooring. Diets were supplemented with 0.25% BW of soybean meal and either no enzyme or 1.5, 3, 4.5, or 6 g of a mixture of a protease with A. oryzae and A. niger fermentation extracts in a calcium carbonate carrier. A 14-d dietary adaptation was followed by 7 d of total fecal collection. On d 21, 3 rumen samples per ewe were taken at 4 h intervals for analysis of pH and VFA concentrations. Data were analyzed using the MIXED procedure of SAS and orthogonal linear and quadratic contrasts were used to assess enzyme dosage effects. Dry matter and ADF digestibility increased quadratically (P < 0.05), and NDF and OM digestibility tended (P ≤ 0.07) to increase quadratically across dosages. Ruminal acetate concentrations decreased quadratically and ruminal propionate increased quadratically (P < 0.05) with increasing enzyme dosage (P < 0.05). Total VFA concentrations were not affected by dosage (P = 0.71), but the acetate:propionate ratio decreased quadratically (P < 0.05) with increasing enzyme dosage. In conclusion, a protease and A. oryzae and A. niger fermentation extract blend increased fiber digestion, but dosages over 3 g of enzyme did not further enhance DMD or DMI.