Effects of roughage concentration in steam-flaked corn-based diets containing wet distillers grains with solubles on feedlot cattle performance, carcass characteristics, and in vitro fermentation

Two studies were conducted to evalu- ate effects of wet distillers grains with solubles (WDG) and dietary concentration of alfalfa hay (AH) on perfor- mance of finishing beef cattle and in vitro fermentation. In both studies, 7 treatments were arranged in a 2 × 3 + 1 factorial; factors were dietary concentrations (DM basis) of WDG (15 or 30%) and AH (7.5, 10, or 12.5%) plus a non-WDG control diet that contained 10% AH. In Exp. 1, 224 beef steers were used in a randomized complete block (initial BW 342 kg ± 9.03) finishing trial. No WDG × AH interactions were observed (P > 0.12). There were no differences among treatments in final shrunk BW or ADG (P > 0.15), and DMI did not differ with WDG concentration for the overall feeding period (P = 0.38). Increasing dietary AH concentration tended (P 0.15) in HCW, dressing percent, LM area, KPH, proportions of cattle grading USDA Choice, and incidence of liver abscesses. In Exp. 2, ruminal fluid was collected from 2 ruminally cannulated Jersey steers adapted to a 60% concentrate diet to evaluate in vitro gas production kinetics, H2S production, IVDMD, and VFA. Relative to the control substrate, including WDG in substrates increased (P 0.09) molar propor- tions or total concentration of VFA. Results indicate that including 15 or 30% WDG in steam-flaked corn- based diets did not result in major changes in feedlot performance or carcass characteristics, but increasing AH concentration from 7.5 to 12.5% in diets contain- ing WDG decreased G:F. Including WDG in substrates decreased rate and extent of gas production and in- creased H2S production. Changes in various measures of in vitro fermentation associated with AH concentra- tions were not large.