Feeding high concentrations of corn dried distillers’ grains decreases methane, but increases nitrous oxide emissions from beef cattle production

Previous research has shown that feeding high fat corn distiller’ grains plus solubles (CDDGS; ∼10% fat, dry matter [DM]) reduces enteric methane (CH4) emission from beef cattle. However, feeding CDDGS (∼30% crude protein [CP] DM) or wheat distillers’ grains plus solubles (WDDGS; ∼40% CP, DM) increases N excretion from beef cattle and the resulting increase in nitrous oxide (N2O) from manure may offset any CH4 mediated decrease in greenhouse gas emissions (GHG). The objective of this study was to evaluate the impact of CDDGS and WDDGS inclusion on GHG emissions from beef cattle using a life cycle assessment (LCA). The LCA was conducted using primary data for diet composition, CH4 emission and N excretion generated in two studies using growing and finishing beef cattle. A representative model farm was simulated using the Holos GHG model (www.agr.gc.ca/holos-ghg), which included 40% DM CDDGS or WDDGS in growing and finishing feedlot diets. The simulation was made relative to the standard practice of using barley grain as the main supplemental energy source in western Canadian beef cattle diets (baseline scenario). Feeding CDDGS (14.98kg CO2 equivalent [CO2e]/kg live weight) and WDDGS (15.41kg CO2e/kg live weight) resulted in 6.2 and 9.3% higher GHG intensity compared to the baseline scenario (14.10kg CO2e/kg live weight). Using high-fat distillers’ grains in the diet of feedlot cattle may decrease enteric CH4 emissions, but at high dietary levels it increases N excretion and results in a net increase in GHG emissions. To reduce environmental impact, dried distillers’ grains should not be included in the diet of feedlot cattle at a level that exceeds N requirements. Manure arising from cattle fed DDGS should be land applied at a level that matches the N requirements of the crop.