148 Supplementing Bovacillus to newly weaned beef steers during a 90-d grazing period

Abstract This experiment compared performance, health, and physiological responses of high-risk stocker cattle receiving a Bacillus subtilis derivative during a 90-d grazing period. Crossbred steers (n = 120) were obtained from an auction yard and transported to the experimental facility. Steer shrunk body weight (BW) was recorded at arrival (d -1). This value was averaged with BW recorded on d 0 to represent initial BW (236 ± 2 kg). On d 0, steers were ranked by BW and allocated to 1 of 12 pastures (4-ha pastures; 10 steers/pasture). Pastures were randomly assigned to receive daily supplementation with dried distillers’ grains at 1% of BW containing either: 1) Bacillus licheniformis and B. subtilis ingredient (BOV; 2 g/steer daily of Bovacillus, Chr Hansen A/S, Horsholm, Denmark) or 2) no additive (CON). Cattle received treatments from d 0 to 90 while housed in pastures containing stockpiled grass forage, as well as free-choice access to water and a commercial mineral + vitamin mix without ionophores. Steers were assessed for bovine respiratory disease (BRD) signs daily, and shrunk BW recorded on d 91. Blood samples were collected, and BW recorded on d 0, 14, 28, 56, and 90. No treatment differences were detected (P ≥ 0.19) for glucose, non-esterified fatty acids, β-hydroxybutyrate, haptoglobin, or insulin-like growth factor 1, whereas a treatment × day interaction indicated increased cortisol in BOV cattle on d 56 (P 0.01). A treatment × day interaction was detected for serum concentrations of parainfluenza type 3 antibodies, which was greater in BOV steers on d 90 (P 0.01). No treatment differences were detected (P ≥ 0.23) for serum concentrations of antibodies against other BRD pathogen. Average daily gain (ADG) tended to be increased (P = 0.09) in BOV compared with CON steers from d 56 to d 90 (0.858 and 0.760 kg/d, respectively, although did not impact overall ADG (P = 0.48). No treatment differences were detected for steer final BW (P = 0.43). Total BW change per pasture was greater in BOV compared with CON (790 vs. 550 kg BW change; P = 0.02). No treatment differences were detected (P = 1.00) for BRD incidence, although steers removed from the experiment for health reasons tended to be increased in CON compared with BOV (P = 0.08). Despite lacking differences in health or physiological responses, B. licheniformis and B. subtilis supplementation increased overall production of BW in high-risk stocker steers during a 90-d grazing period.