Rumen microbial system, methanogenesis, and methane mitigation strategies in ruminants

Abstract

Much of the biomass in this world is rich in fibre which is utilised by the ruminants with the help of rumen microbes to produce a good quality protein for human consumption. However, this conversion of fibre to high-quality protein is paralleled by the production of methane which represents the wastage of feed energy and is a powerful greenhouse gas harmful to the global climate. The microbial community in the rumen has co-evolved with their host animal in a symbiotic relationship over millions of years and methanogenesis has emerged as a result of the refinement of the fermentation process in the rumen. The one-to-one relationship between the methanogen population and the methanogenesis has not been established yet, which indicates the role of associated rumen microbiota, substrate availability, and other functional parameters of the rumen. This review has focused on the total rumen microbial structure, methanogen structure, rumen fermentation process, methanogenesis, factors affecting methane production, and methane mitigation strategies. The balance between the H2 producers and H2 consumers in the rumen determines the level of methane production in the rumen. Therefore, decreasing the availability of H2 in the rumen by fostering alternative H2 sinks, such as propionate production, is very instrumental in reducing the rumen methane emissions. Any strategy of methane abatement should concurrently consider the enhancement of propionate production to prevent the inhibition of rumen functions. Although a great deal of information regarding the rumen microbial community structure, rumen physiology, and methane mitigation strategies is currently available, more research is still needed. The majority of the in vivo experiments pertaining to methane abatement strategies discussed in this review are the short term experiments in which long term unwanted effects could not be precisely predicted. Therefore, there is a need for long-term experiments to draw valid and logical conclusions on the methane abatement strategies.