Effect of dried distillers' grains with solubles on greenhouse gas emissions from beef cattle

Four experiments were conducted to determine the impact of dried distillers' grains with solubles (DDGS) on greenhouse gas (GHG) emissions from beef cattle. The first compared in vitro methane (CH4) production from corn DDGS (CDDGS, ~30% crude protein [CP]) and wheat DDGS (WDDGS, ~40% CP dry matter [DM]). Wheat DDGS or CDDGS replaced barley silage at 20, 40, 60, 80 and 100% DM. Methane (mg CH4/g DM) was lower for CDDGS than WDDGS at up to 80% DM. In a second experiment, heifers fed a growing (high silage) diet showed a reduction in CH4 (g CH4/kg DM intake [DMI]) when 35% barley grain and 5% canola meal DM were replaced with CDDGS (10.0% fat DM). Inclusion of 40% WDDGS (4.1% fat DM) had no effect on enteric CH4 emissions. In contrast, feeding 40% DM WDDGS with added corn oil (9.5% fat DM) reduced CH4 to the same extent as CDDGS. In a third experiment, replacing 40% DM barley grain with CDDGS (9.7% fat DM) in a finishing (high grain) diet reduced CH4 (g/kg DMI). Whereas feeding 40% DM WDDGS along with corn oil (9.9% fat DM) resulted in similar CH4 losses as CDDGS. Results from both in vitro and in vivo experiments indicate that the higher fat content of CDDGS vs. WDDGS was responsible for CH4 reductions. The benefit of replacing 40% DM barley grain with CDDGS or WDDGS on GHG emissions from beef production was further evaluated using life cycle assessment. Replacing barley grain with CDDGS or WDDGS increased N intake and subsequently N excretion. Increased N excretion was predicted to outweigh reductions in CH4 through increased formation of nitrous oxide (N2O). Therefore, feeding CDDGS and WDDGS resulted in 6.3 and 9.3% higher GHG intensity (kg CO2 equivalent [CO2e]/kg beef) compared to the control. To reduce the environmental impact, DDGS should not be fed at inclusion levels that exceed N requirements of feedlot cattle.