Enteric methane emissions in grazing dairy systems

Approximately 80% of agricultural CH(4) comes from livestock systems, with 90% of that derived from enteric CH(4) production by ruminants. Grazing systems are used worldwide to feed dairy cattle. Although quantifying enteric CH(4) 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 CH(4) emissions under various grazing conditions, as well as effective and economic strategies to mitigate CH(4) 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 CH(4) emissions and applicability to pastoral dairy systems. The effects of enteric CH(4) in the broader context of whole-system assessments will be discussed, which are key to assess the overall environmental impact of grazing dairies.