Ruminant Nutrition: Rumen Fermentation Modifiers

The objective of this study was to evaluate the effects of Rumensin and Tylan in feedlot diets containing wet distillers grains plus solubles. Eight hundred beef steers (329 ± 25 kg) were blocked by initial BW and randomly assigned to one of five treatments (20 steers per pen, 8 pens per treatment). Treatments consisted of a corn-based diet with Rumensin and Tylan (CORN+RT) and four treatments with 25% wet distillers grains plus solubles (DG) and either 36.7 mg/kg (R) or 49.0 mg/kg (HIR) of Rumensin and Tylan (T) at 90 mg•hd–1•d–1. Compared to CORN+RT, steers fed DG+RT gained more, were more efficient (P<0.05), and had similar DMI (10.7 vs. 10.6 kg). Feeding Rumensin increased G:F by 3.1% and Rumensin plus Tylan increased G:F by 4.9% when compared to DG alone (P<0.05). With the exception of dressing percentage, there were no differences in performance or carcass characteristics when Rumensin was fed at 36.7 compared to 49.0 mg/kg. Total liver abscesses were significantly greater for DG (42.4%) and DG+R (40.8%), compared to treatments containing Tylan, CORN+RT (17.0%), DG+RT (8.3%), and DG+HIRT (8.9%). Severe liver abscesses were also less for diets containing Tylan (P<0.05). This study indicates that steers fed Rumensin and Tylan in diets containing wet distillers grains plus solubles results in improved feed efficiency and decreased liver abscesses compared to similar diets without these feed additives.