A fibrolytic enzyme additive for lactating Holstein cow diets: ruminal fermentation, rumen microbial populations, and enteric methane emissions.

The objective was to determine if supplementing a dairy cow diet with an exogenous fibrolytic enzyme additive (Econase RDE; AB Vista, Marlborough, Wiltshire, UK) altered fermentation, pH, and microbial populations in the rumen or enteric methane (CH(4)) emissions. In a companion study, this enzyme additive improved efficiency of fat-corrected milk production in a dose-dependent manner by up to 11% for early lactation dairy cows. Nine ruminally cannulated, lactating Holstein cows were used in a replicated 3 × 3 Latin square design with 21-d periods. Dietary treatments were 0 (control), 0.5 (low), and 1.0 (high) mL of enzyme/kg of total mixed ration dry matter. Rumen contents were collected on 2 d (d 15 and 19), ruminal pH was measured continuously for 6 d (d 13 to 18) by using an indwelling system, and enteric CH(4) production was measured for 3 d (d 16 to 18) using the sulfur hexafluoride tracer gas technique. The enzyme additive did not alter volatile fatty acids, NH(3), pH, or population densities of total protozoa, bacteria, and methanogens in ruminal fluid. However, population densities of certain bacteria, calculated as copy number of species-specific 16S-rRNA, were affected by enzyme treatment. Population density of Ruminobacter amylophilus was increased and that of Fibrobacter succinogenes tended to be increased by the high enzyme treatment. Selenomonas ruminantium tended to increase linearly with increasing levels of enzyme in the diet, although its population density was only numerically increased by the high enzyme treatment. Streptococcus bovis, however, tended to be decreased by the low enzyme treatment. Increasing the level of enzyme supplement in the diet also linearly increased enteric CH(4) production, even when adjusted for feed intake or milk production (19.3, 20.8, and 21.7 g of CH(4)/kg of dry matter intake or 12.9, 13.6, and 15.1g of CH(4)/kg of milk for the control, low, and high enzyme treatments, respectively). This shift in ruminal bacterial communities and higher CH(4) emissions could imply increased ruminal digestion of feed, which needs to be substantiated in longer term studies.