Effect of Two Exogenous Fibrolytic Enzyme Preparations on Rumen Fermentation and In Situ Degradability Kinetics in Dairy Cattle
The objective was to compare effects of two Trichoderma reesei exogenous fibrolytic enzyme preparations (EFE) on the ruminal degradation and fermentation of a bermudagrass- and corn silage-based TMR. Endoglucanase and xylanase activities of a moderate xylanase (MIX) and xylanase-rich (XYL) EFE were 2,087 and 2,714 and 10,549 and 26,926 µmol/min per g, respectively. Both EFE improved milk production by lactating dairy cows in previous studies. Three ruminally-cannulated lactating Holstein cows (735 ± 8 kg; 159 ± 47 DIM) were assigned to Control (CON), MIX or XYL treatments in a 3 × 3 Latin square design with 23-d periods. The MIX and XYL EFE were added to the ration of the cows just before feeding at rates of 3.4 and 1 mL/kg of TMR DM, respectively. On d 18 of adaptation, ground (4 mm) samples of the TMR were weighed (5 g of DM) into in situ bags, treated with or without the EFE, and massaged to ensure thorough mixing. Exactly 24 h later, bags were placed in the rumens of the cows for 0, 4, 8, 16, 24, 48 and 72 h. All bags were removed simultaneously, washed, dried, and weighed. An exponential model was fitted to the DM degradation data. On d 23, ruminal fluid was collected from each cow just before feeding and every 2 h afterwards for 10 h and analyzed for fermentation products and pH. The model used to analyze the fermentation data included effects of treatment, time, treatment by time interaction, period and the random effect of cow. A similar model without the time effect was used to analyze the in situ degradability data. Applying EFE had no effect (P > 0.1) on in situ degradability lag phase, washout fraction, potentially degradable fraction, undegradable fraction, or fractional degradation rate of DM. Also, EFE application did not affect (P > 0.1) ruminal pH or concentrations of ammonia-N, total VFA, acetate (A), propionate (P), butyrate, isobutyrate, isovalerate, valerate or the A:P ratio. Adding these EFE to a bermudagrass and corn silage - based TMR did not affect ruminal fermentation or in situ ruminal degradability under the conditions of this study.