AbstractThe objectives of this experiment were to evaluate the effects of feedingBacillus subtilisPB6 on clinical health, performance, and carcass characteristics of feedlot steers.Bos indicuscrossbred 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 dailyB. subtilisPB6 (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 dailyB.subtilisPB6 may improve feed efficiency in feedlot cattle.