Factors affecting methane production and mitigation in ruminants

Methane (CH₄) is the second most important greenhouse gas (GHG) and that emitted from enteric fermentation in livestock is the single largest source of emissions in Japan. Many factors influence ruminant CH₄ production, including level of intake, type and quality of feeds and environmental temperature. The objectives of this review are to identify the factors affecting CH₄ production in ruminants, to examine technologies for the mitigation of CH₄ emissions from ruminants, and to identify areas requiring further research. The following equation for CH₄ prediction was formulated using only dry matter intake (DMI) and has been adopted in Japan to estimate emissions from ruminant livestock for the National GHG Inventory Report: Y = −17.766 + 42.793X − 0.849X², where Y is CH₄ production (L/day) and X is DMI (kg/day). Technologies for the mitigation of CH₄ emissions from ruminants include increasing productivity by improving nutritional management, the manipulation of ruminal fermentation by changing feed composition, the addition of CH₄ inhibitors, and defaunation. Considering the importance of ruminant livestock, it is essential to establish economically feasible ways of reducing ruminant CH₄ production while improving productivity; it is therefore critical to conduct a full system analysis to select the best combination of approaches or new technologies to be applied under long-term field conditions.