Enteric methane emissions in grazing dairy systems

Approximately 80% of agricultural CH4 comes from livestock systems, with 90% of that derived from enteric CH4 production by ruminants. Grazing systems are used worldwide to feed dairy cattle. Although quantifying enteric CH4 emissions in grazing systems has unique challenges, emerging technologies have made gaseous data collection more feasible and less laborious. Nevertheless, robust data sets on enteric CH4 emissions under various grazing conditions, as well as effective and economic strategies to mitigate CH4 emissions in grazing dairy cows, are still in high demand because data collection, feeding management, and milk market regulations (e.g., organic certification, grassfed) impose more challenges to grazing than confinement dairy systems. This review will cover management strategies to mitigate enteric CH4 emissions and applicability to pastoral dairy systems. The effects of enteric CH4 in the broader context of whole-system assessments will be discussed, which are key to assess the overall environmental impact of grazing dairies.