Abstract
Methane generated during enteric fermentation in ruminant livestock species is a major contributor to global anthropogenic greenhouse gas emissions. A period of moderate feed restriction followed by ad libitum access to feed is widely applied in cattle management to exploit the animal’s compensatory growth potential and reduce feed costs. In the present study, we utilised microbial RNA from rumen digesta samples to assess the phylogenetic diversity of transcriptionally active methanogens from feed-restricted and non-restricted animals. To determine the contribution of different rumen methanogens to methanogenesis during dietary restriction of cattle, we conducted high-throughput mcrA cDNA amplicon sequencing on an Illumina MiSeq and analysed both the abundance and phylogenetic origin of different mcrA cDNA sequences. When compared to their unrestricted contemporaries, in feed-restricted animals, the methanogenic activity, based on mcrA transcript abundance, of Methanobrevibacter gottschalkii clade increased while the methanogenic activity of the Methanobrevibacter ruminantium clade and members of the Methanomassiliicoccaceae family decreased. This study shows that the quantity of feed consumed can evoke large effects on the composition of methanogenically active species in the rumen of cattle. These data potentially have major implications for targeted CH4 mitigation approaches such as anti-methanogen vaccines and/or tailored dietary management.
Highlights
The 2015 UNFCCC Paris agreement aims to pursue efforts to limit the increase in global warming to 1.5 °C1 above temperatures prevailing during the pre-industrialisation era[1]
We previously found that feed-restricted animals had increased relative abundance of 16S DNA from the Methanobrevibacter gottschalkii clade[5]
We previously reported, using high-throughput 16S DNA amplicon sequencing, that a period of moderate feed restriction led to greater abundance of M. gottschalkii clade in the ruminal liquor of moderately feed restricted animals with an inverse relationship to a putative Succinivibrionaceae species[5]
Summary
The 2015 UNFCCC Paris agreement aims to pursue efforts to limit the increase in global warming to 1.5 °C1 above temperatures prevailing during the pre-industrialisation era[1]. Following two months of re-alimentation, the volatile fatty acid ratios of ruminal digesta from previously feed restricted animals mirrored that of their non-restricted contemporaries, while a reversal in the relative abundance of 16S DNA from the Methanobrevibacter gottschalkii clade and the putative Succinivibrionaceae 16S DNA5 was observed. It is still not clear if analysis of 16S DNA accurately reflects the metabolic activity of rumen bacteria and archaea as metabolically inactive and dead bacteria retain large amounts of DNA14. This may be useful as a convenient and inexpensive method for use in large numbers of animals to answer the, as yet unanswered question, ‘which methanogens are making the greatest relative contribution to ruminal methane production’?
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