Effect of dried distillers' grains with solubles on enteric methane emissions and nitrogen excretion from finishing beef cattle

The objective of this study was to examine the impact of corn- or wheat-based dried distillers' grains with solubles (CDDGS, WDDGS) on enteric methane (CH4) emissions from finishing beef cattle, and to determine if any observed reductions were a result of the fat content of CDDGS. A second objective was to compare the effect of CDDGS or WDDGS on N excretion. The experiment was designed as replicated 4 x 4 Latin square with 28-d periods using 16 ruminally fistulated crossbred heifers. The control diet contained 87% barley grain, 8% barley silage and 5% supplement (dry matter; DM basis). Treatment diets were formulated by replacing 40% DM of barley grain with CDDGS, WDDGS, or corn oil supplemented WDDGS (WDDGS+oil). For the WDDGS+oil diet 6.5% corn oil was added to WDDGS (3.4% fat DM) to achieve a similar fat level as in CDDGS (9.7% DM). All diets were fed as total mixed rations once daily ad libitum. Total collection of urine and faeces was conducted between days 18 and 21. Methane was measured between days 25 and 28 using four identical open circuit respiratory chambers. Compared with WDDGS, feeding CDDGS and WDDGS+oil reduced (P <0.05) CH4 emissions as a percentage of gross energy intake (GET) from 5.5 to 4.0 and 4.2%, respectively. Feeding CDDGS also reduced (P <0.05) CH4 emissions compared with the control (5.0% of GET), while WDDGS+oil tended (P =0.08) to elicit a similar response. Methane (% of GET) between WDDGS and the control did not differ (P =0.29). Excretion of total N was greater (P <0.001) for CDDGS, WDDGS and WDDGS+oil (220, 253, and 265 g d(-1)) compared with the control (143 g d(-1)). Although oil appears to be responsible for reducing CH4 emissions when DDGS is included in the diet, increased N excretion requires that a complete life cycle assessment be conducted to assess the full impact of DDGS on greenhouse gas emissions from finishing cattle.