Potential and existing mechanisms of enteric methane production in ruminants

Junyi Qiao,Min Wang,Zhiliang Tan

doi:10.1590/0103-9016-2013-0423

Abstract

Enteric methane (CH4) emissions in ruminants have attracted considerable attention due to their impact on greenhouse gases and the contribution of agricultural practices to global warming. Over the last two decades, a number of approaches have been adopted to mitigate CH4 emissions. However, the mechanisms of methanogenesis have still not been fully defined. According to the genome sequences of M. ruminantium in the rumen and of M. AbM4 in the abomasum, the pathways of carbon dioxide (CO2) reduction and formate oxidation to CH4 have now been authenticated in ruminants. Furthermore, in the light of species or genera description of methanogens, the precursors of methanogenesis discovered in the rumen and research advances in related subjects, pathways of acetate dissimilation via Methanosarcina and Methanosaeta as well as metabolism of methanol to CH4 might be present in the rumen, although neither process has yet been experimentally demonstrated in the rumen. Herein the research advances in methanogenesic mechanisms including existing and potential mechanisms are reviewed in detail. In addition, further research efforts to understand the methanogenesis mechanism should focus on isolation and identification of more specific methanogens, and their genome sequences. Such increased knowledge will provide benefits in terms of improved dietary energy utilization and a reduced contribution of enteric CH4 emissions to total global greenhouse gas emissions from the ruminant production system.

Highlights

It is predicted that the global surface temperature will increase between 1 oC to 6 oC during the twentyfirst century, primarily due to the increased emissions of greenhouse gases in the atmosphere
AbM4 in the abomasum, the pathways of carbon dioxide (CO2) reduction and formate oxidation to CH4 have been authenticated in ruminants
In the light of species or genera description of methanogens, the precursors of methanogenesis discovered in the rumen and research advances in related subjects, pathways of acetate dissimilation via Methanosarcina and Methanosaeta as well as metabolism of methanol to CH4 might be present in the rumen, neither process has yet been experimentally demonstrated in the rumen

Summary

Introduction

It is predicted that the global surface temperature will increase between 1 oC to 6 oC during the twentyfirst century, primarily due to the increased emissions of greenhouse gases in the atmosphere. Enteric CH4 emissions contribute to global climate warming, and account for 2 ~ 12 % of the ingested energy. The populations of methanogens range from 107 to 109 g−1 of rumen contents in concentrate-fed ruminants and are up to 109 to 1010 g−1 of rumen contents in pasture-fed ruminants (Attwood et al, 2011) To date, methanogens, such as Methanobrevibacter ruminantium, Methanobrevibacter smithii, Methanobrecibacter millerae, Methanobrevibacter olleyae, Methanobacterium formicicum, Methanobacterium bryantii, Methanosarcina barkeri, Methanosarcina mazai and Methanomicrobium mobile have been isolated by culture methods (Janssen and Kirs, 2008; Sirohi et al, 2010; Kumar et al, 2012).

Ruminal methanogenesis

Findings

Final Remarks