Variations in methane yield and microbial community profiles in the rumen of dairy cows as they pass through stages of first lactation.

Considerable interest exists both from an environmental and economic perspective in reducing methane emissions from agriculture. In ruminants, CH4 is produced by a complex community of microorganisms that is established in early life but can be influenced by external factors such as feed. Although CH4 emissions were thought to be constant once an animal reached maturity, recent studies have shown that CH4 yield significantly increases from early to late lactation in dairy cows. The aim of this study was to test the hypothesis that increases in CH4 yield over the lactation cycle are related to changes in rumen microbial community structure. Nine cows were monitored throughout their first lactation cycle. Methane and dry matter intake were measured to calculate CH4 per dry matter intake (CH4 yield) and ruminal fluid was collected during early, mid, and late lactation. A significant difference in bacterial and archaeal community structure during early and late lactation was observed. Furthermore, when ruminal short-chain fatty acid concentrations were measured, the ratio of acetate and butyrate to propionate was significantly higher in late lactation compared with early lactation. Propionate concentrations were higher in cows with low CH4 yield during late lactation, but no differences were observed in bacterial or archaeal community structures. Prevotella dominated the rumen of cows followed by Succinclasticum; Treponema, Fibrobacter, Ruminococcus, and Bifidobacterium were also in high abundance relative to other bacterial genera. In general, positive correlations were stronger between the most relatively abundant bacterial genera and acetate and butyrate concentrations in the cows with high CH4 and weaker between these genera and propionate concentration. This study indicates that increased CH4 yield in late lactation is reflected in significant changes in microbial community structure.