174. Effects of Feeding a Bacillus-based Probiotic on Performance of Feedlot Cattle Offered a High-concentrate Diet Supplemented with Sodium Monensin.

Abstract Feedlot cattle are often offered dietary feed additives, such as monensin, that support its rumen function. However, additional interest has been given to natural solutions, such as probiotics that may optimize nutrient degradation in the rumen and overall health of the herd. Hence, we hypothesized that adding a Bacillus-based probiotic in a feedlot diet containing monensin sodium would improve performance of the herd. Based on this rationale, our objective was to evaluate the effects of B. licheniformis 809 and B. subtilis 810 supplementation in combination with monensin on performance of feedlot cattle. Four hundred and two steers (initial BW 329 ± 65 kg) were blocked by source and BW into 28 feedlot pens. Then, within block, pens were randomly assigned to a feedlot diet containing monensin (CON; n = 14) or CON with the addition of 2 g/head per day of B. licheniformis 809 and B. subtilis 810 (BAC; n = 14). All animals were offered a receiving diet and two adaptation diets for 7 days each until a transition to a finishing diet for 98 days. The finishing diet contained 11% roughage and 89% concentrate, including 48% and 20% (dry matter basis) of high-moisture corn and dry rolled corn, respectively. Pen fecal score was evaluated weekly throughout the study, while DMI was evaluated daily. Individual BW was evaluated on days 0, 35, and 115 and based on these measurements, ADG and FCR were determined. Animals were slaughtered on days 118 and 121 of the study. All data were analyzed with SAS (version 9.4) and pen was used as the experimental unit. Body weight on days 35 and at the end of the study were greater (P ≤ 0.03) for steers fed BAC, while no differences were observed on DMI (P = 0.70; Table 1). Average daily gain was 7.0 and 3.8% greater (P ≤ 0.03) for BAC on days 35 and 115, respectively, while FCR was also improved by 7.7 and 3.4% in BAC, respectively (P = 0.03). At slaughter, the carcass of BAC-fed steers was heavier (P = 0.05; + 3.5 kg), while P8 fat thickness tended to be greater (P = 0.07). Lastly, mean pen fecal score tended (P = 0.08) to be greater in BAC vs. CON. In summary, adding B. licheniformis 809 and B. subtilis in a feedlot diet containing monensin improved live performance of feedlot cattle offered a high-starch diet when compared with monensin alone. Also, positive effects were also observed in carcass weight, carcass composition, and pen fecal score. These data demonstrate the efficacy and feasibility of adding a Bacillus-based probiotic in feedlot operations. For image description, please refer to the figure legend and surrounding text.