The effect of medicinal feed additive programs and dietary sulfur concentrations in steam-flaked corn diets containing wet distillers grains on performance and carcass merit in yearling feedlot steers1, 2, 3

A total of 432 crossbred yearling steers (329 ± 10.5 kg) were used in an unbalanced randomized block design to examine the effects of a medicinal feed additive (MFA) program and dietary sulfur (S) concentrations on feedlot performance and carcass merit. Treatments were arranged in a 2 × 2 factorial, with main factors being ionophore and antibiotic combination consisting of feed additive program monensin/tylosin or laidlomycin propionate/chlortetracycline and dietary S concentration [constant (CST) or variable (VAR)]. High-S diets (0.60% S) were fed on randomly assigned days to the VAR treatment, with low-S diets (0.48% S) fed on remaining days and to the CST treatment throughout the experiment. No interactions between S and MFA treatment were apparent for feedlot performance. Steers receiving VAR had greater (P < 0.05) BW than did CST-supplemented steers. Overall, DMI was greater (P < 0.05) for VAR than for the CST steers. Average daily gain and feed efficiency did not differ between CST and VAR. Steers receiving VAR diets had a mortality rate attributable to polioencephalomalacia 7.8 times greater (P < 0.02) than that of steers fed CST diets. Feedlot performance and carcass merit did not differ between the MFA treatments, and S treatment did not affect most carcass variables. The S × MFA interaction was significant (P < 0.05) for DP, such that S treatment had no effect on DP when monensin/tylosin was fed, but when steers were fed laidlomycin propionate/chlortetracycline, DP was decreased by 0.72% (P < 0.02) when VAR diets were fed. These results suggest that under our conditions, performance and carcass characteristics were not affected by MFA treatment. Furthermore, varying S concentration in finishing diets increased mortality rate; however, feedlot performance and carcass measurements were generally not affected by S treatment.