171. Feed Smarter: Bacillus Based Direct Fed Microbial Supplementation Improves Feed Intake and Reduces Stress Markers in Feeder Calves.

Abstract The animal industry faces growing pressure to improve production efficiency and animal health while reducing environmental impacts and ensuring product safety. Within this context, the use of biotics, commonly referred to as probiotics or direct-fed microbials (DFM), has gained increasing attention due to their capacity to enhance nutrient digestion, reduce morbidity and mortality, alleviate stress-related responses, and improve growth performance and feed efficiency. Given these benefits, our research and others have evaluated the effects of supplementing a Bacillus-based DFM (BAC; Bovacillus™; Novonesis, Hørsholm, Denmark) during the most physiologically and nutritionally challenging phases of the beef cattle production cycle, when feeder cattle are exposed to multiple stressors, including weaning, transportation, commingling, and dietary transitions at feedlot entry. Across compiled studies, BAC supplementation in forage based diets or total mixed rations (TMR) was associated with a 3.4% increase in dry matter intake relative to non supplemented cattle. In our initial studies evaluating BAC supplementation in cattle (n = 15) consuming a forage based diet, intake increased by 4% compared with non supplemented cattle (15.5 vs. 14.9 kg/d; P < 0.01). In this study, cattle supplemented with BAC increased DM and CP digestibility by 3.4 and 5.7% compared with CON, respectively. Digestibility of NDF and ADF tended to increase by 2.7 and 2.4%, respectively. In addition, Bacillus based DFM supplementation increased the total amounts of DM, CP, NDF, and ADF digested by 13.6, 16.4, 11.9, and 11.6%, respectively. These results are consistent with the compiled studies, showing increases of 3.9%, 6.5%, and 5.1% in DM, CP, and NDF digestibility, respectively, when cattle are supplemented with BAC. In another study from our group, supplementing BAC during the receiving phase for beef calves (n = 84) tended to increase DMI compared with the CON group (P = 0.06), without affecting other performance parameters (P ≥ 0.50). A treatment × day interaction was observed for plasma cortisol concentration (P < 0.01), with CON animals exhibiting greater cortisol concentrations on d 14. Mean plasma haptoglobin concentration was greater in CON compared with BAC calves (P = 0.03). Collectively, these results indicate that Bacillus based DFM supplementation increased feed intake and nutrient digestibility while reducing circulating stress markers in feeder calves during a receiving period, supporting its potential use as a nutritional strategy during challenging phases of the feeder cattle production cycle.