The rumen microbiome of yak co-evolves with its host probably adding the adaptation to its harsh environments

Abstract Background Rumen microbes play an important role in ruminant energy supply and animal performance. Previous studies showed that yak (Bos grunniens) rumen microbiome and fermentation differ from other ruminants. However, little is understood on the features of the rumen microbiome that make yak adapted to its unique environmental and dietary conditions. Here we investigated the rumen microbiome and metabolome to understand how yak adapts to the coarse forage and harsh environment in the high Qinghai-Tibetan plateau. Result Metataxonomic analysis of the rumen microbiota revealed that yak (Bos grunniens), domesticated cattle (Bos taurus), and dzo (a hybrid between the yak and domestic cattle) have distinct rumen microbiota. Metagenomic analysis displayed a larger gene pool encoding a richer repertoire of carbohydrate-active enzymes (CAZymes) in the rumen microbiome of yak and dzo than cattle. Some of the genes encoding glycoside hydrolases (GH) that mediate the digestion of cellulose and hemicellulose were significantly enriched in the rumen of yak than cattle, but the cattle rumen microbiome had more genes assigned to GH57 that primarily includes amylases. The rumen fermentation profile differed also, with cattle having a higher molar proportion of acetate but a lower molar proportion of propionate than dzo and yak. Metabolomic analysis showed differences in both rumen microbial metabolic pathways and metabolites, mainly amino acids, carboxylic acids, sugars, and bile acids. Notably, styrene degradation, primary bile acid biosynthesis, glyoxylate, and dicarboxylate metabolism significantly differed between cattle and dzo; streptomycin biosynthesis was significantly different between cattle and yak; and the pathways for biotin metabolism and styrene degradation significantly differed between dzo and yak. Correlation analysis revealed certain microbial species correlated with differential rumen metabolites. Nine differential metabolites showed a positive correlation with seven species belonging to Bacteroides and Alistipes but a negative correlation with ten species belonging to Prevotella and Ruminococcus. Conclusion The present study showed that the rumen microbiome of yak and its host had probably co-evolved aiding in the adaptation of yak to the harsh dietary environment of the Qinghai-Tibetan plateau. In particular, the yak rumen microbiome has more enzymes involved in the degradation of rough forage than that of cattle, providing sufficient energy for its host.