Effects of feeding CLOSTAT ( Bacillus subtilis PB6) on the clinical health, performance, and carcass characteristics of feedlot steers 1 .

The objectives of this experiment were to evaluate the effects of feeding Bacillus subtilis PB6 on clinical health, performance, and carcass characteristics of feedlot steers. Bos indicus crossbred steer calves ( n = 397; 342 kg initial body weight [BW]) were randomly assigned to pens by initial BW; pens ( n = 24) were randomly assigned to one of two of the following experimental treatments: 1) no supplemental dietary direct-fed microbial, control (CON; n = 12 pens) or 2) 13 g/steer daily B. subtilis PB6 (CLO; CLOSTAT, Kemin Industries, Des Moines, IA; n = 12 pens). Steers were housed in 12.2 × 30.5 m soil-surfaced pens; pen served as the experimental unit. The percentage of cattle treated once or twice for bovine respiratory disease (BRD) did not differ among treatments ( P ≥ 0.27); BRD mortality also did not differ between CON and CLO ( P = 0.34). During the receiving period, final BW ( P = 0.97), average daily gain (ADG; P = 0.91), dry matter intake (DMI; P = 0.77), and gain:feed ( P = 0.79) were not different among treatments. There was a tendency ( P = 0.09) for CLO-supplemented steers to be 14% more efficient from days 0 to 14 of the receiving period. Final BW, overall finishing phase ADG, and DMI did not differ by treatment ( P ≥ 0.14); ADG was 0.14 kg greater for CLO than CON ( P = 0.03) from days 29 to 56 of the finishing period. Gain: feed tended ( P = 0.07) to be 7% greater (0.144 vs. 0.141) for CLO than CON throughout the duration of the finishing period, and 6.7% greater ( P = 0.08; 0.152 for CLO vs. 0.150 for CON) for the entirety of the experiment. Carcass traits did not differ among treatments ( P ≥ 0.31). The results of this experiment suggest that supplementing 13 g/steer daily B . subtilis PB6 may improve feed efficiency in feedlot cattle.