Synergistic Adaptations of Yak Rumen Microbiota, Metabolites and Host to Altitudinal

Rumen microbiota and metabolites play important roles in energy metabolism and immune regulation in the host. However, the underlying mechanisms of their interaction with the host to regulate yak plateau adaptation remain unknown. In this study, the effects of altitude on the rumen microbiome, metabolome, and fermentation parameters of yaks were analyzed. The fiber content of pasture grasses increased with altitude, while crude protein content was significantly higher at an altitude of 2800 m (T2800) compared to an altitude of 4500 m (T4500) (p < 0.05). The acetic acid, propionic acid, and volatile fatty acids of yaks in the T4500 group were significantly higher than in the T2800 group (p < 0.05). Simpson's index of rumen microorganisms in the T4500 group of yaks was significantly higher than in T2800 and T3500 yaks. The relative abundance of Rikenellaceae_RC9_gut_group and Succiniclasticum was significantly higher in T4500 than in T2800, while Prevotella and Streptococcus were more abundant in T2800 than in T4500. Rumen metabolomics analyses revealed that yak rumen metabolites at different altitudes were influenced by forage and altitude, mainly affecting energy metabolism and fatty acid biosynthesis (such as purine and glycerophospholipid metabolism). In summary, altitude may influence rumen microbes and metabolites through pasture nutrient composition.