Forage Type and Exogenous Fibrolytic Enzyme Application Rate Effects on the Digestibility of Dairy Cattle Forages

Abstract Text: The objective was to examine the effects of applying two Trichoderma reesei exogenous fibrolytic enzyme products (EFE) at different application rates on the in vitro DM (DMD) and NDF (NDFD) digestibility of bermudagrass silage, a 50:50 alfalfa -orchardgrass hay mixture and corn silage. Treatments were a Xylanase-rich EFE (XYL), a 25:75 mixture of XYL and a cellulase EFE (MIX), and an untreated Control. Endoglucanase and xylanase activities of MIX and XYL were 2,087 and 2,714 and 10,549 and 26,926 µmol/min per g, respectively. The EFE were diluted in water and applied in quadruplicate to the substrate at 0, 0.5, 1, 4, and 8 μl of EFE/g of DM. The suspensions were incubated at 25°C for 24 h before addition of buffered-rumen fluid (39°C) and further incubation for 24 h in two runs. Rumen fluid was obtained from 3 lactating dairy cows fed TMR containing all of the tested forages. Data were analyzed as a completely randomized design with a 2 × 5 × 3 factorial treatment arrangement. The optimal dose was defined as the application rate with the highest digestibility that was higher (P < 0.05) than lower doses. Optimal doses of XYL and MIX for improving bermudagrass silage DMD were 0.5 (58.2 vs. 55.2 %) and 1 (58.4 vs. 55.2 %) μl/g, and those for increasing NDFD were 4 (39.7 vs. 32.9 %) and 0.5 (36.7 vs. 32.9 %) μl/g, respectively. For alfalfa / orchardgrass hay, respective optimal doses for DMD were 1 (68.8 vs. 66.0 %) and 0.5 (68.7 vs. 66.0 %) μl/g and those for NDFD were 1 (29.6 vs. 22.9 %) and 0.5 (27.2 vs. 22.9%) μl/g, respectively. For corn silage, the respective optimal doses for DMD were both 1 μl/g (62.8 and 64.1 vs. 60.7 %) and for NDFD they were both 4 μl/g (25.5 and 25.3 vs. 16.3 %). Both XYL and MIX increased the in vitro DMD and NDFD of bermudagrass silage, alfalfa / orchardgrass hay and corn silage. Optimal application rates for improving DMD and NDFD differed across substrates for each EFE. The XYL and MIX EFE increased milk production by dairy cows when applied 1 and 3.4 μl/g of TMR DM, respectively in a subsequent trial.

Keywords: forage, enzyme, dose