LAUSR

Abstract An experiment was conducted comparing medicated feed additives (MFA) bambermycin or monensin sodium and tylosin phosphate in feedlot diets containing modified distillers grains (mDGS). Crossbred steers (n = 256; initial full BW 418 ± 28.5 kg) were allocated into three weight blocks in a randomized complete block design with a 2 × 2 factorial arrangement of treatments. The factors were: MFA (bambermycin at 20 mg/steer daily or monensin + tylosin at 380 and 90 mg/steer daily, respectively) and mDGS inclusion (15% and 30% of diet DM). Twenty-four pens were utilized, resulting in six replications per treatment. Steers were fed a diet consisting of a 1:1 combination of dry-rolled and high-moisture corn with the roughage portion of the diet consisting of corn silage and corn stover. Steers in the heaviest two blocks were marketed after 104 d and steers in the lightest block were marketed after 126 d. Overall average daily gain (ADG) tended (P = 0.08) to be greater for bambermycin vs. monensin and tylosin, and was not affected (P = 0.17) by mDGS level. Dry matter intake was lower (P ≤ 0.05) with 30% mDGS with monensin and tylosin than with any other treatment. Feed efficiency was not affected by mDGS, MFA, or their interaction (P ≥ 0.30). Marbling scores were greater (P = 0.01) greater for bambermycin vs. monensin and tylosin, and tended (P = 0.08) to be greater with 15% mDGS than with 30% mDGS. Carcasses from steers fed bambermycin had a greater percentage of USDA choice than those fed with monensin and tylosin (P = 0.01). Liver abscess occurrence was not affected (P ≥ 0.17) by MFA, mDGS, or their interaction. Results from this experiment indicate that including bambermycin in feedlot diets containing 30% mDGS results in increased DMI when compared with including monensin and tylosin in 30% mDGS diet without the risk for increases in liver abscess occurrence.