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Background: Heifers emit more enteric methane (CH 4 ) than adult cows and these emissions tend to decrease per unit feed intake as they age. However, common mitigation strategies like expensive high-quality feeds are not economically feasible for these pre-production animals. Given its direct role in CH 4 production, altering the rumen microbiota is another potential avenue for reducing CH 4 production by ruminants. However, to identify effective microbial targets, a better understanding of the rumen microbiota and its relationship to CH 4 production across heifer development is needed., Results: Here, we investigate the relationship between rumen bacterial, archaeal, and fungal communities as well as CH 4 emissions and a number of production traits in prepubertal (PP), pubertal (PB), and pregnant heifers (PG). Overall, PG heifers emitted the most CH 4 , followed by PB and PP heifers. The bacterial genus Acetobacter and the archaeal genus Methanobrevibacter were positively associated, while Eubacterium and Methanosphaera were negatively associated with raw CH 4 production by heifers. When corrected for dietary intake, both Eubacterium and Methanosphaera remained negatively associated with CH 4 production., Conclusion: We suggest that Eubacterium and Methanosphaera represent likely targets for CH 4 mitigation efforts in heifers as they were negatively associated with CH 4 production and not significantly associated with production traits. © 2018 Society of Chemical Industry., (© 2018 Society of Chemical Industry.)

The evaluation of how the gut microbiota affects both methane emissions and animal production is necessary in order to achieve methane mitigation without production losses. Toward this goal, the aim of this study was to correlate the rumen microbial communities (bacteria, archaea, and fungi) of high (HP), medium (MP), and low milk producing (LP), as well as dry (DC), Holstein dairy cows in an actual tropical production system with methane emissions and animal production traits. Overall, DC cows emitted more methane, followed by MP, HP and LP cows, although HP and LP cow emissions were similar. Using next-generation sequencing, it was found that bacteria affiliated with Christensenellaceae, Mogibacteriaceae, S24-7, Butyrivibrio, Schwartzia, and Treponema were negatively correlated with methane emissions and showed positive correlations with digestible dry matter intake (dDMI) and digestible organic matter intake (dOMI). Similar findings were observed for archaea in the genus Methanosphaera. The bacterial groups Coriobacteriaceae, RFP12, and Clostridium were negatively correlated with methane, but did not correlate with dDMI and dOMI. For anaerobic fungal communities, no significant correlations with methane or animal production traits were found. Based on these findings, it is suggested that manipulation of the abundances of these microbial taxa may be useful for modulating methane emissions without negatively affecting animal production., (Copyright © 2017 Elsevier GmbH. All rights reserved.)