129. Bacillus-based Direct-fed Microbials Supplementation Alters Blood Stress Markers in Feeder-calves During a 60-day Feedlot Receiving Program

Abstract Stress factors such as weaning and transport, combined with changes in the environment and diet, can lead the stocker cattle to immunosuppression, impacting the animal health, welfare, and consequently performance. Supplementation with Bacillus-based direct-fed microbials (DFM) has demonstrated efficacy in promoting ruminal and gastrointestinal health while increasing intake and performance in beef cattle. Therefore, our hypothesis and objective were that supplementing Bacillus-based DFM during a 60-day feedlot receiving program would mitigate blood stress-related markers in feeder-calves. Eighty-four recently weaned Angus calves were sourced from Virginia Tech's Kentland Farm in Blacksburg, VA, and transported to the farm's feedlot facility on day -1. On d 0, calf body weight (BW) was recorded after 16 h of feed and water withdrawal to use as initial BW. Calves (BW = 279.62 ± 7.4 kg and age = 233 ± 6 days) were ranked by BW, age, and sex in a completely randomized design and then allocated to one of 20 drylot pens (4 to 5 calves per pen; 5 × 9 m; 2.5 m linear of feed bunk), and assigned to receive 1 of 2 treatments: 1) a total mixed ration (TMR) plus 165 g of protein-mineral supplement + 3 g of a Bacillus-based DFM containing Bacillus licheniformis and B. subtilis (BAC; n = 10; 2.2 × 109 CFU of the mixture/g; Bovacillus, Novonesis, Lyngby, Denmark), or 2) a TMR plus 165 g of protein-mineral supplement without DFM (CON; n = 10). Blood samples were collected via jugular venipuncture on days 0, 7, 14, 21, 28, 42, and 56 using commercial 10 mL Vacutainer tubes (Becton Dickinson, Franklin Lakes, NJ), containing freeze-dried sodium heparin, for plasma concentration analysis of stress-related biomarkers and metabolites. A treatment × day interaction was observed (P = 0.01) for plasma concentration of cortisol (Table 1). Calves receiving BAC supplementation had lower (P = 0.01) plasma cortisol concentration compared to the control group on day 14 (Fig. 1). The overall plasma haptoglobin concentration was reduced (P = 0.03) in BAC compared with CON calves (Table 1). No treatment effects were observed for plasma glucose (P = 0.32), serum non-esterified fatty acids (NEFA, P = 0.25), and beta-hydroxybutyrate (BHBA, P = 0.87). In summary, supplementation with Bacillus-based DFM decreased plasma cortisol and haptoglobin concentrations of calves, which might lead to a better feedlot environment adaptation, welfare, and performance during a feedlot receiving program.