Effect of method of adding a fibrolytic enzyme to dairy cow diets on feed intake digestibility, milk production, ruminal fermentation, and blood metabolites

Abstract

This study investigated the effect of the method of applying a fibrolytic enzyme (Promote®; Cargill; Minnetonka, MN) on the performance of lactating dairy cows. A diet consisting of Tifton 85 bermudagrass silage, corn silage, and concentrate (35, 10 and 55% of dietary DM respectively) was fed ad libitum as a total mixed ration (TMR) twice daily. Cows were assigned randomly to the following five treatments: 1) control (no enzyme added), enzyme applied 2) at ensiling to bermudagrass (ES), 3) at mixing to the concentrate (EC), 4) at feeding to the TMR (ETMR), or 5) the bermudagrass silage (EF). In Experiment 1, thirty Holstein cows (129 days in milk, DIM) were used in a completely randomized, cross-over design consisting of two 28-d periods, with 14 d for adaptation and 14 d for sample collection. Voluntary DMI, total tract apparent digestibility of DM, NDF and CP, milk production and component yields were not affected by enzyme supplementation. Cows fed ETMR had lower blood β-hydroxybutyrate concentration, tended to have greater milk fat and protein concentrations and lower blood urea-N concentration than cows fed the control diet. In Experiment 2, five ruminally-cannulated cows were fed the same five diets for three consecutive 15-d periods to measure rumen fermentation (d 12) and in situ degradation (d 14 and 15). Compared to cows fed the control diet, ruminal pH tended to be lower in cows fed EC and ruminal NH3-N concentration was lower in cows fed the ETMR diet. The molar proportion of acetic acid was lower in cows fed ETMR and EF diets vs. the control diet. Total volatile fatty acid concentration and acetate: propionate ratio were lower in cows fed ETMR vs the control diet. Enzyme application did not affect in situ degradability except that the ES diet tended to degrade at a faster rate than the control diet. Enzyme application to the TMR gave the most desirable responses (tended to increase milk fat and protein concentrations and improved the efficiency of ruminal energy utilization and decreased ruminal protein degradation). However, enzyme addition did not affect intake, digestibility or milk yield.