International Symposium on Ruminant Physiology: The role of rumen microbiome in the development of methane mitigation strategies for ruminant livestock.

Ruminants play an important role in global food security and nutrition. The rumen microbial community provides ruminants with a unique ability to convert human indigestible plant matter into high quality edible protein. However, enteric CH produced in the rumen is both a potent GHG and a ME loss for ruminants. As the rumen microbiome constitutes 15% to 40% of the interanimal variation in enteric CH emissions, understanding the microbiological mechanisms underpinning ruminal methanogenesis and its interaction with the host animal is crucial for developing CH mitigation strategies. Variation in the relative abundance of different microbial species has been observed in cattle with contrasting residual CH emission and CH yield, with up to 20% of the variation in interanimal CH emissions attributable to the presence of a small number of microbial species. The demonstration of ruminotypes associated with high or low CH emissions suggests that interactions within complex microbial consortia and with their host are a major source of variation in CH emissions. Consequently, microbiome-assisted genomic approaches are being developed to select low CH-emitting cattle, with breeding values for enteric CH being included as part of national breeding programs. Generating rumen microbiome data for use in selection programs is expensive, therefore, identifying microbial biomarkers in milk or plasma to develop predictive models which include microbial predictors in equations based on animal-related data is required. A better understanding of the rumen microbiome has also aided the development and refinements of antimethanogenic feed additives. However, these strategies, which increase the amount of reducing equivalents in the rumen ecosystem, do not generally result in an enrichment of propionate or an improvement in animal performance. Current research aims to provide alternative sinks to reducing equivalents and to stimulate activity of commensal microbes or the supplementation of direct fed microbials to capture lost energy. Furthering our knowledge of the rumen microbiome and its interaction with the host will aid in the development of CH mitigation strategies for ruminant livestock.