Response of lactating dairy cows to a cellulase and xylanase enzyme mixture applied to forages at the time of feeding.

Fifty Holstein cows (20 primiparous and 30 multiparous) were used in an experiment to evaluate the dose response to a direct-fed cellulase and xylanase enzyme mixture applied to the forage portion (60% corn silage and 40% alfalfa hay) of a total mixed ration just prior to feeding. Cows were fed one of five treatment diets for 12 wk. Diets 1 through 4 were 55% forage: 45% concentrate and consisted of an untreated control and the control diet plus 0.7, 1.0, or 1.5 L of enzyme concentrate/tonne of forage dry matter, respectively. Diet 5 was an untreated 45% forage: 55% concentrate diet. Actual production of milk increased as much as 10.8% relative to the control diet with 1.5 L of enzyme, and production of fat and protein increased as much as 20 and 13%, respectively. The lowest concentration of enzyme treatment (0.7 L/tonne) accounted for approximately one-half of the production increases. The responses to enzyme-treated forages occurred 2 to 4 wk after the cows started to consume the treated forages, and the same responses were maintained throughout the remainder of the experiment. Cows that started to receive enzyme-treated forage during the first 100 d postpartum produced 9 to 15% more milk and 16 to 23% more energy-corrected milk than did cows fed the control diet. However, production was not increased when cows were in midlactation at the start of the experiment. Responses to enzyme-treated forages fed in 55: 45 forage to concentrate rations were similar to the response to increased proportions of concentrates fed with untreated forages at the 45:55 forage to concentrate ratio.