Mitigation of enteric methane emissions from global livestock systems through nutrition strategies

Enteric methane (CH4) generated in the gastrointestinal tract of ruminant represents the source of the greatest direct greenhouse gas (GHG) released from the livestock sector. We evaluated the global potential reduction of enteric CH4 emissions released from dairy cattle through amendment of their traditional diets in 183 countries aggregated to 11 regions. Amending dairy cattle diets involves increasing the concentration of lipid (up to 6 %) and decreasing the concentration of fiber, without affecting the total gross energy intake (GEI). Enteric CH4 emissions were calculated by using a mathematical model developed to include dietary intervention. In 2012, we found a global potential reduction of 15.7 % of enteric CH4 emissions from dairy cattle. The highest potential reduction per unit of milk produced occurs in Africa followed by South America and Asia (55, 46 and 34 %, respectively). The amended diets proposed here, mostly affect the regions in which demand for animal source protein will be greatest in the future. Because lipid supplementation may result in an indirect effect on CH4 and nitrous oxide (N2O) emissions from manure management, they were also estimated. Methane emissions from manure management would decrease by 13 %, while N2O emissions would increase by 21 % due to diet amendment. On balance, the total potential reduction of GHG emissions through diet amendment was 104 MtCO(2)eq annually. Moreover, amending diets would increase global milk production by 13 %. This study evaluated a global potential reduction of GHG emissions directly released from dairy cattle, however, future advancements dealing with the analysis of the upstream emissions associated to these diet changes are needed.