A comparison of methods of adding fibrolytic enzymes to lactating cow diets.

Holstein cows (n = 43) in early lactation were used to investigate effects of method of adding fibrolytic enzymes to diets on feed intake, milk production, and digestibility. Cows were blocked according to parity and calving date and randomly assigned to three treatments: control, enzymes applied to the total mixed ration (E-TMR), or enzymes added to the barley-based concentrate (E-Conc). The enzyme product used was a proprietary blend that contained relatively high xylanase and low cellulase activities (Biovance Technol. Inc., Omaha, NE). An enzyme solution (50 mg of enzyme powder dissolved into 20 ml of water) was sprayed onto each kilogram of total mixed ration (dry matter basis) before feeding. Alternatively, 73 g of enzyme powder, dissolved in 20 L of water, was added per ton of concentrate (50 mg of enzyme/kg of diet dry matter). The total mixed rations contained 24% corn silage, 14% alfalfa hay, and 62% concentrate (dry matter basis) and were offered ad libitum. In vitro gas production assays and two experiments using sheep were conducted to measure the effects of enzyme treatment on digestibility. Dry matter intake (mean: 19.8 kg/d) was not affected by enzyme supplementation. Milk yield (kg/d) was higher for cows fed E-Conc (37.4) than for cows fed control (35.3) or E-TMR (35.2) with no effects on milk composition. Total tract digestibility (%) of dry matter was higher for E-Conc (66.6%) than for the control diet (63.9%) and intermediate for E-TMR (65.7%) when measured in dairy cows. However, the digestibility of the diets was substantially higher when measured in sheep than in dairy cows, with no effects of enzyme supplementation. The results indicate that fibrolytic enzymes have the potential to increase digestibility and milk production in dairy cows because digestion is low relative to potential digestibility. When digestion is higher, as was observed in lambs or in vitro, no improvement in digestibility occurs. Method of enzyme delivery must also be considered to maximize the benefits of using fibrolytic enzymes in dairy cow diets.