Two studies were conducted to evaluate effects of dried distillersgrains with solubles (DDGS) and alfalfa hay (AH) or corn silage(CS) on feedlot performance, carcass characteristics, ruminalfermentation, and diet digestibility in cattle fed steam-flakedcorn (SFC) diets. In trial 1, crossbred heifers (n = 358; BW= 353 ± 13 kg) were used in a finishing trial to evaluateinteractions between corn-DDGS and roughage source (AH or CS)in terms of impact on feedlot performance and carcass characteristics.Experimental diets (DM basis) consisted of SFC and 11% CS withoutDDGS (SFC-CS), SFC and 11% CS with 25% DDGS (DDGS-CS), SFC and6% AH without DDGS (SFC-AH), and SFC with 25% DDGS and 6% AH(DDGS-AH). Heifers were fed for ad libitum intake once dailyfor 97 d. Results indicated no interaction between DDGS androughage source with respect to animal performance. FeedingDDGS did not affect ADG (P = 0.19), DMI (P = 0.14), or feedconversion (P = 0.67). Heifers fed CS had greater DMI than thosefed AH (P = 0.05), but ADG (P = 0.56) and G:F (P = 0.63) werenot different. There were no differences among treatments withrespect to HCW, dressing percentage, subcutaneous fat thickness,quality grades, or yield grades (P > 0.20). Cattle fed CStended (P = 0.10) to have greater marbling scores than thosefed AH. There was an interaction (P = 0.02) between roughageand DDGS with respect to incidence of liver abscess. The greatestincidence was observed in cattle fed diets without DDGS whenCS was fed, and the least was observed in cattle fed diets withoutDDGS when AH was used. In the second trial, ruminal fermentationcharacteristics and diet digestibility were examined in 12 cannulatedHolstein steers fed similar diets to those fed in the finishingtrial. Ruminal pH for all treatments was below 5.8 for 14 hafter feeding. Acetate:propionate ratios were less (P = 0.02)in steers fed 25% DDGS but had greater (P = 0.02) ruminal lactateconcentrations compared with cattle fed 0% DDGS. Feeding 25%DDGS decreased (P < 0.01) ruminal ammonia concentrations,and digestion of DM and OM was less (P < 0.01) compared withdiets without DDGS. The decrease in digestibility was largelyattributable to decreases in digestion of CP (P = 0.03) andNDF (P < 0.01). Feeding strategies aimed at increasing ruminalpH and ruminally available protein may improve digestion ofDDGS in steam-flaked corn-based finishing diets.