Effects of increasing level of corn distillers dried grains with solubles on intake, digestion, and ruminal fermentation in steers fed seventy percent concentrate diets

Five ruminally and duodenally cannulated steers (500 +/- 5 kg of initial BW) were used in a 5 x 5 Latin square to evaluate effects of increasing level of corn distillers dried grains with solubles (DDGS) in growing diets (70% concentrate) on OM intake, site of digestion, ruminal fermentation, and microbial efficiency. Diets consisted of 30% grass hay, 6% concentrated separator by-product, 4% supplement, and 60% dry-rolled corn, sunflower meal, urea, or DDGS (DM basis). Treatments consisted of increasing DDGS at 0, 15, 30, 45, or 60% of diet DM replacing a combination of dry-rolled corn, sunflower meal, and urea. Diets were balanced for growing steers gaining 1.22 kg/d and included 0.25% (DM basis) chromic oxide as a digesta flow marker. Diets were offered to the steers for ad libitum intake each day (10% above the intake of the previous day). Each period consisted of 14 d for adaptation and 7 d for collections. Intake of OM responded quadratically (P = 0.004) with greatest intakes at 15% DDGS and least at 60% DDGS. No differences (P >= 0.14) were observed in CP intake or duodenal flow of OM, CP, and NDF. Apparent and true ruminal OM digestibilities decreased (linear; P <= 0.009) with increasing DDGS inclusion. Total tract CP digestibility increased (linear; P < 0.001) with increasing DDGS, but total tract OM digestibility was not different (P = 0.74). Microbial efficiency (g of microbial N/kg of OM truly fermented) was not affected (P = 0.22) by treatment. As DDGS increased, ruminal pH increased (linear; P = 0.004), whereas ammonia concentration remained unchanged (P = 0.42). Acetate proportions decreased (linear; P < 0.001) with increasing DDGS, whereas propionate and butyrate were not affected (P >= 0.19). A cubic (P = 0.02) effect was observed for total ruminal fill (as is basis) with the greatest fill at 0% DDGS and the least fill at 45% inclusion. Replacing dry-rolled corn with up to 60% DDGS in 70% concentrate diets resulted in no adverse effects on total tract OM digestion, although OM intake was reduced at 60% DDGS inclusion.