172. Supplementing a Bacillus-based Probiotic to Mitigate Frothy Bloat in Beef Cattle Receiving a High-concentrate Diet.

Abstract This experiment compared the incidence of frothy bloat as well as ruminal, physiological, and performance responses of beef heifers receiving a bloat-provoking diet and supplemented with a Bacillus-based probiotic (BAC; Bacillus licheniformis + B. subtilis; Bovacillus; Novonesis, Lyngby, Denmark). Sixteen ruminally cannulated yearling Angus-influenced heifers were ranked by pre-trial body weight (BW) and assigned to 2 groups of 8 heifers each. Groups were enrolled in a 2 × 2 Latin square design consisting of 2 periods of 28 d with a 14-d washout interval between periods. Groups were assigned to receive no BAC supplementation (CON; n = 16) or BAC supplementation at 3.0 g/heifer daily (BAC; n = 16) from d 0 to 28. During each period, heifers were housed in individual pens and offered a sorghum-based bloat-provocative diet at 2% of BW (DM basis). Diet and treatments were individually fed twice daily in equal portions at 0700 and 1600 h. Heifer unshrunk BW was recorded on d − 3, −2, and −1 relative to the beginning of each period and averaged to determine initial BW, whereas final BW was calculated from the average BW recorded on d 26, 27, and 28. Heifers were assessed for bloat score (0 to 5 scale; increasing according to bloat severity) daily at 3 h after the morning feeding. Rumen fluid samples were collected via rumen cannula on d 0 and 28 of each period immediately before (0 h) and at 3, 6, and 9 h relative to the morning feeding. Results obtained on d 0 were averaged and used as covariates. No treatment differences were detected (P ≥ 0.45) for BW gain or gain:feed ratio. Mean bloat score during the experiment did not differ between treatments (1.15 vs. 1.16 for BAC and CON heifers, respectively; SEM = 0.95; P ≥ 0.59). Rumen pH on d 28 also did not differ between BAC and CON heifers (5.83 vs. 5.80; SEM = 0.06; P ≥ 0.59). Heifers assigned to BAC had lower (P = 0.04) rumen fluid viscosity compared with CON heifers (3.15 vs. 3.89 mPa·s; SEM = 0.32). In addition, BAC heifers had reduced (P = 0.05) ruminal protozoa counts on d 28 compared with CON heifers (8.53 × 10⁵ vs. 1.02 × 106 cells/mL; SEM = 7.0 × 104). Heifers assigned to BAC also had lower (P = 0.03) ruminal valerate concentrations compared with CON heifers (4.41 vs. 5.21 mM; SEM = 0.55), whereas no other treatment effects were detected (P ≥ 0.14) for individual or total volatile fatty acid concentrations. Collectively, supplementing BAC to beef heifers consuming a sorghum-based bloat-provocative diet decreased rumen fluid viscosity and protozoa population, but did not improve rumen fermentation parameters or mitigate the incidence of frothy bloat.