Two Different Bacterial Community Types Are Linked with the Low-Methane Emission Trait in Sheep

Abstract

<div><p>The potent greenhouse gas methane (CH₄) is produced in the rumens of ruminant animals from hydrogen produced during microbial degradation of ingested feed. The natural animal-to-animal variation in the amount of CH₄ emitted and the heritability of this trait offer a means for reducing CH₄ emissions by selecting low-CH₄ emitting animals for breeding. We demonstrate that differences in rumen microbial community structure are linked to high and low CH₄ emissions in sheep. Bacterial community structures in 236 rumen samples from 118 high- and low-CH₄ emitting sheep formed gradual transitions between three ruminotypes. Two of these (Q and S) were linked to significantly lower CH₄ yields (14.4 and 13.6 g CH₄/kg dry matter intake [DMI], respectively) than the third type (H; 15.9 g CH₄/kg DMI; <i>p</i><0.001). Low-CH₄ ruminotype Q was associated with a significantly lower ruminal acetate to propionate ratio (3.7±0.4) than S (4.4±0.7; <i>p</i><0.001) and H (4.3±0.5; <i>p</i><0.001), and harbored high relative abundances of the propionate-producing <i>Quinella ovalis</i>. Low-CH₄ ruminotype S was characterized by lactate- and succinate-producing <i>Fibrobacter</i> spp., <i>Kandleria vitulina</i>, <i>Olsenella</i> spp., <i>Prevotella bryantii</i>, and <i>Sharpea azabuensis</i>. High-CH₄ ruminotype H had higher relative abundances of species belonging to <i>Ruminococcus,</i> other Ruminococcaceae, Lachnospiraceae, Catabacteriaceae, <i>Coprococcus</i>, other Clostridiales, <i>Prevotella</i>, other Bacteroidales, and Alphaproteobacteria, many of which are known to form significant amounts of hydrogen. We hypothesize that lower CH₄ yields are the result of bacterial communities that ferment ingested feed to relatively less hydrogen, which results in less CH₄ being formed.</p></div