PSIII-12 Bacillus-based direct-fed microbials enhanced reproductive success of Bos indicus-influenced beef heifers.

Abstract This 2-yr study evaluated the impacts of Bacillus-based direct-fed microbials (DFM) supplementation on growth and reproduction of Bos indicus-influenced beef heifers. On day 0 of each year (30 days after weaning), Brangus beef heifers (n = 64 per yr) were stratified by body weight (BW; 261 ± 29 kg) and age (286 ± 11 days of age) and randomly allocated into 1 of 16 bahiagrass (Paspalum notatum) pastures (1 ha and 4 heifers per pasture). Treatments were randomly assigned to pastures (8 pastures per treatment). Treatments consisted of daily supplementation of concentrate at 1.50% of BW (dry matter, DM, basis), which included (BAC) or not (CON) a mixture of Bacillus-based DFM (3 g per heifer per day; Bovacillus™; Novonesis, Lyngby, Denmark) from day 0 to 244. Heifers were estrus-synchronized from day 98 to 112. Heifers were inseminated (AI) 12 h after estrus detection from day 109 to 112. Heifers not detected in estrus were timed AI on day 112. All heifers were exposed to Angus bulls from day 119 to 210 (1 bull/pasture). Growth and reproductive performance data were analyzed using MIXED and GLIMMIX procedures of SAS, respectively, and included pasture (treatment × year) as experimental unit and heifer(pasture) as random effect. Effects of treatment ´ year were not detected (P ≥ 0.12) for any variable in the study. Effects of treatment ´ day were not detected (P ≥ 0.83) for herbage mass, herbage allowance, and heifer BW. Heifer average daily gain from day 0 to 109 (0.76 ± 0.02 vs. 0.77 ± 0.02 kg/day, respectively) and mature BW at the start of the breeding season (68.9 ± 0.4% vs. 69.1 ± 0.4%, respectively) did not differ (P ≥ 0.56) between BAC and CON heifers. Percentage of pubertal heifers on day 60 (25 vs. 12 ± 5%, respectively) was greater for BAC vs. CON heifers. Reproductive tract scores on day 60 and 90, and percentage of pubertal heifers on day 90 and heifers detected in estrus from day 109 to 112 did not differ (P ≥ 0.27) between BAC vs. CON heifers. Conception rate to AI (53.3 vs. 40.9 ± 6.4%, respectively), but not final pregnancy rates (P = 0.84; 72.4 vs. 73.3 ± 8.4%, respectively), tended to be greater (P = 0.10) for BAC vs. CON heifers. In summary, despite the similar growth performance, beef heifers supplemented with Bacillus-based DFM had greater puberty attainment prior to estrus synchronization and greater conception rate to AI compared to cohorts offered no DFM supplementation.