Host genetics and the rumen microbiome jointly associate with methane emissions in dairy cows

Cattle and other ruminants produce large quantities of methane (~110 million metric tonnes per annum), which is a potent greenhouse gas affecting global climate change. Methane (CH 4 ) is a natural by-product of gastro-enteric microbial fermentation of feedstuffs in the rumen and contributes to 6% of total CH 4 emissions from anthropogenic-related sources. The extent to which the host genome and rumen microbiome influence CH 4 emission is not yet well known. This study confirms individual variation in CH 4 production was influenced by individual host (cow) genotype, as well as the host’s rumen microbiome composition. Abundance of a small proportion of bacteria and archaea taxa were influenced to a limited extent by the host’s genotype and certain taxa were associated with CH 4 emissions. However, the cumulative effect of all bacteria and archaea on CH 4 production was 13%, the host genetics (heritability) was 21% and the two are largely independent. This study demonstrates variation in CH 4 emission is likely not modulated through cow genetic effects on the rumen microbiome. Therefore, the rumen microbiome and cow genome could be targeted independently, by breeding low methane-emitting cows and in parallel, by investigating possible strategies that target changes in the rumen microbiome to reduce CH 4 emissions in the cattle industry.