Effects of direct-fed microbials supplementation on in vitro and ex vivo ruminal fermentation and nutrient degradability in lactating Holstein dairy cows.

We conducted two experiments to evaluate the effect of direct-fed microbials (DFM) on fermentation parameters and nutrient degradability with two different approaches using rumen fluid from lactating Holstein dairy cows. In Exp. 1, three doses of a DFM containing Lactobacillus animalis and Propionibacterium freudenreichii (PRO-A) at doses of 3.9 × 10⁶, 7.8 × 10⁶, and 11.7 × 10⁶ CFU or a DFM containing PRO-A, Bacillus subtilis, and B. licheniformis (PRO-B) at doses of 15.2 × 10⁶, 30.4 × 10⁶, and 45.6 × 10⁶ CFU were incubated using corn silage as substrate and pooled rumen fluid from three-rumen fistulated lactating Holstein cows. Dry matter and NDF degradability, gas production, and rumen pH were measured over a 24-h period. In Exp. 2, three ruminally cannulated multiparous cows (165 ± 63 DIM) were used in a 3 × 3 Latin square design. Each experimental period was of 28 d. All cows received a corn silage-based TMR (basal diet), and were assigned to: 1) Control (CON), 2) PRO-A: Basal diet top-dressed with PRO-A at 3 × 10⁹ CFU/day, and 3) PRO-B: Basal diet top-dressed with PRO-B at 11.8 × 10⁹ CFU/day. An ex vivo study (Exp. 2) was conducted using rumen fluid collected during wk 4 of each experimental period from experimental animals. Treatments included: CON, PRO-A, PRO-B, each of which utilized rumen fluid from donor cows given respective treatments. Another set of rumen fluid from PRO-A and PRO-B cows were dosed with additional dose of respective DFM, resulting in two more treatments (PRO-A+ and PRO-B+). In Exp. 1, linear effects (P = 0.03) were observed on in vitro NDF degradability following DFM incubation. In Exp. 2, no treatment effects were observed on DM and NDF digestibility. In summary, DFM increased DM and NDF degradability in vitro using rumen fluid from cows not exposed to DFM; however, no effects were observed under ex vivo experimental conditions when rumen fluid was collected from cows consuming DFM.