INVITED REVIEW: Methane sources, quantification, and mitigation in grazing beef systems

Abstract

Purpose: The purpose of the review was to examine enteric methane emissions, quantification methods, and mitigation strategies in grazing beef systems. Sources: Peer-reviewed literature and conference abstracts were the main sources of information for this review. Synthesis: Methane emissions (CH4) can be reduced by improving forage quality by including more cool-season forages and legumes and rotationally grazing animals. Including forages with beneficial secondary compounds such as condensed tannins and saponins also has CH4-mitigation potential. Providing nutritional supplements that improve the nutritional status of the animal and the efficiency of feed energy use has the potential to reduce CH4 emissions from grazing cattle. Genetic selection has shown some viability in reducing herd emissions, but heritability estimates are low for CH4 yield. More research is needed to understand the potential. Soil methanotrophy may partially offset CH4 emissions when animals are stocked moderately but soil CH4 uptake rates are relatively low in most grazing ecosystems. A new metric to quantify the global warming potential of CH4, GWP*, may allow future models to more appropriately consider the behavior and effects of CH4 in the atmosphere. Conclusions and Applications: Methane mitigation strategies in grazing environments are limited, but producer decisions that improve the nutritional status of animals, the quality of the forage base, and supplementation of known CH4-mitigation compounds can reduce CH4 production. Now that less expensive, easier to use quantification tools exist, researchers need to conduct more long-term monitoring experiments and focus on reducing CH4 production of grazing animals where potential for reduction is largest.