Feeding amylolytic and proteolytic exogenous enzymes: Effects on nutrient digestibility, ruminal fermentation, and performance in dairy cows

摘要

Exogenous enzymes are added to diets to improve nutrient utilization and feed efficiency. A study was conducted to evaluate the effects of dietary exogenous enzyme products with amylolytic (Amaize, Alltech) and proteolytic (Vegpro, Alltech) activity on perfor-mance, excretion of purine derivatives, and ruminal fermentation of dairy cows. A total of 24 Holstein cows, 4 of which were ruminally cannulated (161 +/- 88 d in milk, 681 +/- 96 body weight, and 35.2 +/- 5.2 kg/d of milk yield), were blocked by milk yield, days in milk, and body weight, and then distributed in a replicated 4 x 4 Latin square design. Experimental periods lasted 21 d, of which the first 14 d were allowed for treatment adaptation and the last 7 d were used for data collec-tion. Treatments were as follows: (1) control (CON) with no feed additives, (2) amylolytic enzyme product added at 0.5 g/kg diet dry matter (DM; AML), (3) amylolytic enzyme product at 0.5 g/kg of diet DM and proteolytic enzyme product at 0.2 g/kg of diet DM (low level; APL), and (4) amylolytic enzyme products added at 0.5 g/kg diet DM and proteolytic enzyme product at 0.4 g/kg of diet DM (high level; APH). Data were analyzed using the mixed procedure of SAS (version 9.4; SAS Institute Inc.). Differences between treatments were analyzed by orthogonal contrasts: CON versus all enzyme groups (ENZ); AML versus APL+APH; and APL versus APH. Dry matter intake was not affected by treatments. Sorting index for feed particles with size <4 mm was lower for ENZ group than for CON. Total-tract apparent digestibility of DM and nutrients (organic matter, starch, neutral detergent fiber, crude protein, and ether extract) were similar between CON and ENZ. Starch digestibility was greater in cows fed APL and APH treatments (86.3) compared with those in the AML group (83.6). Neutral detergent fiber digestibility was greater in APH cows compared with those in the APL group (58.1 and 55.2, respec-tively). Ruminal pH and NH3-N concentration were not affected by treatments. Molar percentage of propionate tended to be greater in cows fed ENZ treatments than in those fed CON. Molar percentage of propionate was greater in cows fed AML than those fed the blends of amylase and protease (19.2 and 18.5, respectively). Purine derivative excretions in urine and milk were similar in cows fed ENZ and CON. Uric acid excre-tion tended to be greater in cows consuming APL and APH than in those in the AML group. Serum urea N concentration tended to be greater in cows fed ENZ than in those fed CON. Milk yield was greater in cows fed ENZ treatments compared with CON (32.0, 33.1, 33.1, and 33.3 kg/d for CON, AML, APL, and APH, respectively). Fat-corrected milk and lactose yields were higher when feeding ENZ. Feed efficiency tended to be greater in cows fed ENZ than in those fed CON. Feeding ENZ benefited cows' performance, whereas the effects on nutrient digestibility were more pronounced when the combination of amylase and protease was fed at the highest dose.