Effects of supplementing a Bacillus-based direct-fed microbial on ex vivo fermentation traits and on performance of lactating Holstein dairy cows

Three studies evaluated the effects of a Bacillus-based direct-fed microbial (DFM) on ex vivo fermentation traits, as well as on performance of lactating dairy cows. In experiment 1, rumen-fistulated lactating Holstein-Friesian cows (6.6 ± 2.3 parity; 630 ± 37.2 kg BW; 18.9 ± 3.35 kg milk/d) were fed an unsupplemented ration (CON; n = 5) or supplemented with 3 g/cow per d of a Bacillus-based DFM (BAC; n = 5) for 14 d before rumen sampling and subsequent ex vivo evaluation of fermentation characteristics of 2 different substrates (vetch hay [Vicia sativa] and perennial ryegrass herbage [Lolium perenne L.]). Total gas production, methane (CH₄), VFA, and rumen ammonia-N were determined after 24 h of fermentation. In experiment 2, 60 Holstein cows (mean ± SD; 61 ± 3 DIM) fed a 39:61 forage-to-concentrate TMR were assigned to CON or BAC (3 g/cow daily for 13 wk; n = 30 cows per group). In experiment 3, 76 Holstein cows (25 ± 3 DIM) fed a 55:45 forage-to-concentrate TMR were assigned to CON or BAC (3 g/cow daily for 12 wk; n = 38 cows per group). Dry matter intake, milk yield, milk composition, and feed efficiency were evaluated for both experiments 2 and 3. Data from all experiments were analyzed using mixed-effects models. In experiment 1, ruminal concentrations of total VFA, as well as molar proportions of butyrate, isovalerate, valerate, acetate-to-propionate ratio, and NH₃-N increased in BAC compared with CON. In contrast, molar proportions of acetate and propionate were lower for BAC than for CON. Gas production was increased in BAC when adjusted for the amount of DM incubated without affecting CH₄ production. In experiment 2, DMI decreased for both groups starting at wk 7 of the study, but BAC cows consumed less feed than CON cows from wk 8 to 11 and at wk 13. As a consequence, feed efficiency was greater for BAC than for CON cows from wk 5 to 11 and at wk 13 of the study. In experiment 3, mean DMI, milk yield, ECM yield, and milk TS yield were greater in BAC than in CON cows. Altogether, these results indicate that feeding a Bacillus-based DFM is a feasible alternative to promote dairy cow productivity, likely through beneficial changes in ruminal fermentation.