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

SIMPLE SUMMARY: Numerous enteric methane (CH(4)) mitigation opportunities exist to reduce enteric CH(4) and other greenhouse gas emissions per unit of product from ruminants. Research over the past century in genetics, animal health, microbiology, nutrition, and physiology has led to improvements in dairy and beef cattle production. The objectives of this review are to evaluate options that have been demonstrated to mitigate enteric CH(4) emissions per unit of products (energy-corrected milk, milk yield, average daily gain, dry matter intake, and gross energy intake) from dairy and beef cattle on a quantitative basis and in a sustained manner, and to integrate approaches in feeding, rumen fermentation profiles, and rumen microbiota changes to emphasize the understanding of these relationships between enteric CH(4) emissions and animal productivities. ABSTRACT: 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.