An evaluation of exogenous enzymes with amylolytic activity for dairy cows

摘要

An experimental (7B) and commercial (AMA) formulation of enzymes, both primarily with alpha-amylase activity, were evaluated for activity at various pH, stability in ruminal fluid, the potential to improve in vitro ruminal fermentations and the potential to improve production performance of lactating cows. When incubated (40°C) in buffer with a pH between 5.4 and 6, 7B had about 10-25 times more amylase activity than AMA and enzyme activity in this range increased by 100% for 7B whereas activity decreased by about 26% for AMA. Both formulations maintained enzyme activity when they were incubated in in vitro ruminal fermentations. After 6 h of ruminal in vitro fermentations, additions of 7B resulted in linear increases in apparent total volatile fatty acid production for flint and dent corn but had no effect on floury corn. In the first of two lactation trials, 28 Holstein cows (68 +/- 31 days in milk, 46.9 +/- 9.1 kg milk/d) were fed a total mixed ration supplemented with nothing (CTRL), a low dose of 7B (7BL, 0.88 ml/kg total mixed ration dry matter [TMR DM]), a high dose of 7B (7BH, 4.4 ml/kg TMR), or AMA (0.4 g/kg TMR DM). These doses supplied 5,635, 28,176 and 94 Ceralpha units of amylase activity per kg of ration TMR (DM basis) for 7BL, 7BH and AMA, respectively. The experiment was conducted as a 4 x 4 Latin square design with 21-d periods. Cows fed 7BL produced more milk than cows fed CTRL and 7BH but produced similar amounts to cows fed AMA. The production of 3.5% fat corrected milk was greater from cows fed 7BL and AMA when compared to CTRL. The percentage of milk fat and milk protein were unaffected by treatment. Cows fed 7BL, 7BH, and AMA ate similar amounts of DM and cows fed the latter two diets consumed more dry matter than did cows fed CTRL. Cows fed 7BL had a greater apparent total tract digestion of DM, organic matter, and neutral detergent fiber when compared to the CTRL and 7BH diets but digestion of these components were similar to cows fed AMA. In a second lactation trial, cows (84 +/- 51 days in milk, 40.6 +/- 6.8 milk kg/d, mean +/- standard deviation) were fed a TMR supplemented with 7B at 0.5 ml/kg TMR DM (7B1), 1.0 ml/kg TMR DM (7B2), 2.0 ml/kg TMR DM (7B3), or nothing (CON) in a 4 x 4 Latin square design with 21-d periods. Enzymes had no effects on milk production, milk components, or digestibility of feed but diets provided excess nutrients relative to requirements. Cows that were fed a high dose of the experimental amylase (7B3) consumed more feed compared to cows fed CON, but DM intake of 7B3 was similar to cows fed 7B1 and 7B2. The formulations of amylase enzymes evaluated in this study have the ability to increase animal performance but their effectiveness is dependent on one of many factors including the dose at which the enzyme is applied.