Archaeal abundance in post-mortem ruminal digesta may help predict methane emissions from beef cattle

Methane produced from 35 Aberdeen-Angus and 33 Limousin cross steers was measured in respiration chambers. Each group was split to receive either a medium- or high-concentrate diet. Ruminal digesta samples were subsequently removed to investigate correlations between methane emissions and the rumen microbial community, as measured by qPCR of 16S or 18S rRNA genes. Diet had the greatest influence on methane emissions. The high-concentrate diet resulted in lower methane emissions (P , 0.001) than the medium-concentrate diet. Methane was correlated, irrespective of breed, with the abundance of archaea (R 5 0.39), bacteria (20.47), protozoa (0.45), Bacteroidetes (20.37) and Clostridium Cluster XIVa (20.35). The archaea5bacteria ratio provided a stronger correlation (0.49). A similar correlation was found with digesta samples taken 2–3 weeks later at slaughter. This finding could help enable greenhouse gas emissions of large animal cohorts to be predicted from samples taken conveniently in the abattoir.