Methanogenesis and Its Strategic Mitigation through Dietary Intervention and Rumen Manipulation: a Review

Methanogenesis is the formation of methane facilitated by a group of organisms from the phylum Archaea. There are three types of methanogenic Archaea depending on the substrate they use as input metabolite. The hydrogenotrophic (use H2), methylotrophic (use methylated compound), and acetoclastic (utilize acetate) methanogens. These are a biological process where rumen methanogens consume a substrate from fermentation mainly H2 to obtain energy where CH4 is the by-product. This enteric methane emission from livestock is both an environmental concern (greenhouse gases) and a production inefficiency as methane output is considered an energy loss. This paper reviews an understanding of methanogenesis and the application of approaches that could maximize production and reduce the release of pollutants under animal agriculture. The type and ratio of carbohydrates could alter the number and presence of microbes due to variations in rumen pH and substrates contained, such structural carbohydrates favor the growth of propionate-forming microbes that affect the rate of methanogenesis. An increase in the propionate ratio indicates a low methane emission as H2 is redirected away from the creation of methane. Phytochemicals from plants (oil, tannins, saponins) have direct and indirect effects on methanogens, while they also lower the numbers of protozoa that play a significant role in transferring molecular hydrogen, which will be utilized for methanogenesis. Novel rumen modulators like 3-nitrooxypropanol inhibit the methyl coenzyme M reductase (MCR) necessary for methane synthesis and have a remarkable potential to mitigate CH4. Other strategies include breeding performance, food waste minimization, change in diet preferences, housing and culling, etc. are also ways to decrease methane output. However, there is still a need to validate its effects on animal performance, residues in food, feasibility, availability, and economic grounds.