Effect of exogenous fibrolytic enzymes on ruminal fermentation and nutrient digestion in dairy cows

The aim of the present study was to examine the effects of an exogenous fibrolytic enzyme product applied to a total mixed ration (TMR) prior to feeding on ruminal fermentation, microbial protein synthesis, nutrient digestion, and milk yield and composition. Six multiparous lactating Holstein cows (598 +/- 29 kg initial live weight and 98 +/- 30 days in milk) fitted with rumen and duodenal cannulae were allocated to two treatments in a crossover design over three consecutive 28-d periods. The TMR containing 50% concentrates, 30% corn silage and 20% grass silage on dry matter (DM) basis, was mixed once daily and fed twice a day. Treatments were TMR alone (Control) or TMR with an enzyme product containing primarily cellulase and xylanase activities (9000 U endo-1,4-beta glucanase, 24000 U endo-1,3(4)-beta glucanase and 40000 U 1,4-beta xylanase per ml). The enzyme product was applied at a rate of 6.2 ml/kg TMR (DM basis). It was diluted at a rate of 1:5 with water and applied daily to the TMR. During the control period the cows received a TMR supplemented with 36 ml water/kg TMR on DM basis. Duodenal digesta flow was measured using Cr2O3 as flow marker and microbial protein in the duodenal digesta was estimated by near-infrared spectroscopy (NIRS). There were no significant differences in ruminal pH-values, NH3-N concentrations, total SCFA concentrations and molar proportions of SCFA. No treatment effects on microbial N flow to the duodenum and efficiency of microbial protein synthesis were observed. The apparent ruminal digestibilities of DM, organic matter, NDF and ADF, milk yield and composition were also not affected by the enzyme supplementation. In this study the application of exogenous fibrolytic enzymes fed to dairy cows did not show a significant effect on any parameter tested.