Enteric Methane Emissions and Animal Performance in Dairy and Beef Cattle Production: Strategies, Opportunities, and Impact of Reducing Emissions.

Enteric methane (CH 4 ) emissions produced by microbial fermentation in the rumen resulting in the emission of greenhouse gases (GHG) into the atmosphere. The GHG emissions reduction from the livestock industry can be attained by increasing production efficiency and improving feed efficiency, by lowering the emission intensity of production, or by combining the two. In this work, information was compiled from peer-reviewed studies to analyze CH 4 emissions calculated per unit of milk production, energy-corrected milk (ECM), average daily gain (ADG), dry matter intake (DMI), and gross energy intake (GEI), and related emissions to rumen fermentation profiles (volatile fatty acids [VFA], hydrogen [H 2 ]) and microflora activities in the rumen of beef and dairy cattle. For dairy cattle, there was a positive correlation ( p < 0.001) between CH 4 emissions and DMI ( R 2 = 0.44), milk production ( R 2 = 0.37; p < 0.001), ECM ( R 2 = 0.46), GEI ( R 2 = 0.50), and acetate/propionate (A/P) ratio ( R 2 = 0.45). For beef cattle, CH 4 emissions were positively correlated ( p < 0.05-0.001) with DMI ( R 2 = 0.37) and GEI ( R 2 = 0.74). Additionally, the ADG ( R 2 = 0.19; p < 0.01) and A/P ratio ( R 2 = 0.15; p < 0.05) were significantly associated with CH 4 emission in beef steers. This information may lead to cost-effective methods to reduce enteric CH 4 production from cattle. We conclude that enteric CH 4 emissions per unit of ECM, GEI, and ADG, as well as rumen fermentation profiles, show great potential for estimating enteric CH 4 emissions.