PSIX-27 Supplementing a Bacillus-based probiotic improves rumen digestibility and fermentation responses in growing beef heifers.

Abstract This experiment evaluated the effects of a Bacillus-based probiotic (BAC; Bacillus licheniformis + B. subtilis; BovacillusTM; Novonesis, Lyngby, Denmark) on feed intake, in situ ruminal degradability, rumen fermentation and microbiota responses of beef heifers consuming a forage-based diet. Fifteen ruminally-cannulated Angus-influenced heifers were ranked by body weight (BW; 303 ± 7 kg) and assigned to receive no BAC supplementation (CON; n = 7), or BAC at 3.0 g/day (n = 8). During the experiment (day 0 to 35), heifers were housed in individual pens and received water and bermudagrass hay (Cynodon dactylon) for ad libitum consumption, in addition to 1.270 g/d (as-fed basis) of a corn-based concentrate. The BAC was mixed daily with the concentrate and offered to BAC heifers from day 5 to 35. Blood samples were collected on days 0, 7, 14, 21, 28, and 35 (4 h after feeding). Rumen fluid samples were collected on days 0, 14, and 28 (4 h after feeding). Ruminal in situ disappearance parameters of forage dry matter (DM) and neutral detergent fiber (NDF) were evaluated by incubating polyester bags with 4 g of dietary hay on day 32 for 96 h. Data were analyzed using heifer as experimental unit, and values from day 0 as covariate when appropriate. Hay intake did not differ between treatments (P = 0.59). Heifers supplemented with BAC had less (P = 0.02) acetate:propionate in the rumen fluid (3.97 vs. 4.44). Heifers supplemented with BAC had less (P ≤ 0.05) prevalence of the bacterial genera Bacteroides, Pedobacter, and Ruminococcus, but greater (P = 0.05) prevalence of Paludibacter in the rumen. Heifers supplemented with BAC tended to have greater ruminal disappearance rate of hay DM (3.36 vs. 2.65 %/h) and NDF (4.00 vs. 3.10 %/h), and had (P ≤ 0.05) greater effective degradability of hay DM (42.3 vs. 40.2%) and NDF (52.0 vs. 50.1). Heifers supplemented with BAC had greater (P = 0.02) mean plasma concentrations of glucose (72.7 vs. 68.9 mg/dL) and less (P < 0.01) mean plasma concentration of urea N (5.63 vs. 6.62 mg/dL). Collectively, BAC supplementation improved rumen digestibility and fermentation responses in growing beef heifers consuming a forage-based diet.