Implications of farm-scale methane mitigation measures for national methane emissions

Agriculture contributes ~40% of the total UK’s emissions of methane (CH4), mostly from enteric fermentation by ruminant livestock, with a smaller contribution associated with manure management. A number of CH4 mitigation measures have been identified, but their effectiveness over broad spatial scales had not previously been investigated. Another question was whether widespread implementation would have consequences on production levels and emissions of other pollutants, such as ammonia (NH3), nitrous oxide (N2O), or leaching of nitrate (NO3-). This project brought together models from rumen processes to individual animals, at the herd, farm and national scale for the first time. Emissions of CH4, NH3, N2O, NOx and NO3- leaching were quantitatively assessed for dairy cattle, beef cattle and sheep. Increasing milk yield in dairy cows (with associated reduction in numbers) results in the largest decrease in CH4, with comparable decreases in N pollutants >20%. For beef cattle and sheep, the most effective CH4 mitigation method is vaccination to reduce rumen methanogens (-10%).