Supplementing a Bacillus-based Probiotic to Mitigate Acidosis in Beef Cattle Consuming a High-concentrate Diet.

This experiment evaluated ruminal fermentation, nutrient degradability, and performance responses of beef heifers receiving an acidosis-inducing diet and supplemented with a Bacillus-based probiotic (BAC; Bacillus licheniformis + B. subtilis; Bovacillus; Novonesis, Lyngby, Denmark). Fifteen ruminally cannulated heifers were ranked by pre-trial body weight (BW) and assigned to 3 groups of 5 heifers each. Groups were enrolled in a replicated 3 × 3 Latin square design with 3 periods of 21 d and a 14-d washout interval between periods. During each period, heifers had ad libitum access to water and were offered a forage-based diet from d 0 to 6, followed by an acidosis-inducing diet from d 7 to 21 at 2% of BW (DM basis), provided in equal portions at 0700 and 1600 h. Groups were assigned to one of three treatments: no BAC supplementation (CON; n = 15), BAC supplementation at 3 g/heifer daily from d 7 to 21 (BAC; n = 15), or BAC supplementation at 3 g/heifer daily from d 0 to 21 (BACPRE; n = 15). The BAC dose was mixed with dried distillers’ grains and manually blended into the diet at each feeding. 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 19, 20, and 21. Rumen fluid samples were collected on d 0, 7, 14, and 21 of each period immediately before (0 h) and at 3, 6, and 9 h after the morning feeding. Dietary dry matter and nutrient degradability in the rumen were evaluated from d 17 to 20 using Ankom bags. No treatment differences were detected (P ≥ 0.20) for BW gain, feed intake, or gain:feed ratio. Likewise, no treatment effects or interactions involving treatment were detected (P ≥ 0.33) for rumen pH. On d 7, concentrations of individual and total volatile fatty acids (VFA) did not differ among treatments (P ≥ 0.15). On d 14, heifers assigned to BAC had lower (P = 0.03) butyrate concentrations compared with BACPRE and CON heifers, whereas no other differences were detected (P ≥ 0.41) for individual or total VFA. On d 21, heifers assigned to BAC and BACPRE had greater (P = 0.03) valerate concentrations than CON heifers, with no additional differences detected (P ≥ 0.36). Heifers assigned to BAC and BACPRE had greater (P ≤ 0.02) diet dry matter disappearance rate and effective degradability compared with CON heifers. In summary, supplementing BAC to beef heifers receiving an acidosis-inducing diet increased ruminal dry matter disappearance rate and effective degradability, but did not modify rumen pH or overall volatile fatty acid concentrations.