Optimization of rumen function for decreasing enteric methane: A conceptual framework

Livestock contribute to 32 % of methane production from the agriculture sector. To limit global warming to under 1.5 °C, it is imperative to decrease methane emissions. While various approaches have been investigated, two strategies are receiving particular attention at present: a) additives that inhibit methane-producing enzymes (e.g. 3-Nitrooxypropanol and seaweeds), and b) rumen microbial ecosystem modifiers (e.g. probiotics and plant secondary metabolites). However, the potential of rumen fermentation optimization towards enteric methane reduction has been underexplored and rarely discussed. This report quantifies decrease in enteric methane and increase in microbial mass production achievable through optimized rumen fermentation. The estimates are derived from: (a) substrate requirements for short-chain fatty acid production according to Wolin's stoichiometry of carbohydrate fermentation, (b) ATP generated during these conversions, and (c) variations in microbial mass synthesis efficiency with ATP utilization. The results suggest a reduction of 30–35 % enteric methane and doubling of microbial mass production. The advantages of optimizing rumen fermentation over the approaches using the inhibitors and phytogenic compounds, e.g. enhanced animal productivity and farmers' income; reduced nitrogen excretion; and enhanced animal health, welfare and immunity are presented. Furthermore, the narrative presented is that optimization of rumen fermentation is a pre-requisite for eliciting higher effects of other approaches and must not be neglected. Triple-gains of higher livestock productivity, reduced enteric methane and greater profitability can be achieved sustainably through this approach.