Evaluation of Protein in Distillers Grains on Site and Extent of Digestion in Finishing Diets

Six ruminally and duodenally fistulated steers were utilized in an unbalanced 6 × 6 Latin square with six periods and four treatments to evaluate the relative contribution of excess rumen undegradable protein from modified distillers grains plus solubles (MDGS) on site and extent of nutrient digestion. The protein from MDGS was evaluated using corn gluten meal to provide similar protein as 40% MDGS. Treatments included: 1) control diet (CON) containing 75.5% dry-rolled corn (DRC), 15% corn silage, 3.5% soybean meal, and 6% supplement; 2) modified distillers grains plus solubles (MDGS40) with 40% MDGS, 39% DRC, 15% corn silage, and 6% supplement; 3) corn gluten meal (CGM) with 17.5% corn gluten meal, 61.5% DRC, 15% corn silage, and 6% supplement; 4) corn gluten meal plus condensed distillers solubles (CGM-CDS) with 17.5% corn gluten meal, 10% condensed distillers solubles, 51.5% DRC, 15% corn silage, and 6% supplement. Condensed distillers solubles was added to CGM to mimic the nutrient profile of distillers grains from cellulosic ethanol production. Dry matter intake was greatest (P ≤ 0.08) for MDGS40 and least (P ≤ 0.10) for CON. Total tract digestibilities of DM and OM were lower (P ≤ 0.03) for steers fed MDGS40 compared to CON, CGM, and CGM-CDS (OM digestibilities of 72.9, 84.7, 80.5, and 84.3%, respectively; SEM = 3.1%). Intake of NDF (P < 0.01) for MDGS40 compared to CON, CGM, and CGM-CDS (2015, 992, 973, and 1001 g / d, respectively; SEM = 88.9 g / d). Total tract NDF digestibility was not different (P = 0.64) among treatments. No difference (P ≥ 0.55) was observed in apparent or true OM ruminal digestibilities. Duodenal flow of NDF was greatest (P ≤ 0.01) for MDGS40 compared to CON, CGM, CGM-CDS (977, 484, 541, 462 g / d, respectively; SEM = 100.1 g / d). Post-ruminal OM digestibility was not different (P > 0.36) among treatments. Ruminal pH had an hour × treatment interaction (P < 0.01) and suggests the minimum ruminal pH of steers consuming CGM-CDS was greater 2 hrs to 9 hrs post-feeding compared to other treatments. In conclusion, feeding MDGS at 40% (DM inclusion) increased DM and NDF intake with decreased total tract digestibility relative to diets containing corn or corn gluten meal. As expected, protein from distillers grains is not the cause of lower digestibility.