Alterations in Rumen Bacterial Community and Metabolome Characteristics of Cashmere Goats in Response to Dietary Nutrient Density

SIMPLE SUMMARY: Dietary energy and protein play important roles in rumen fermentation. However, the impacts of dietary energy and protein on the relationships between rumen bacterial composition and ruminal metabolites were not extensively studied. In this study, we investigated the rumen fermentation status in response to different energy and protein levels, which was vital for the rumen health and resulted in the potential positive effects on the host health and production. Thereby, quantitative polymerase chain reaction analysis and 16S rRNA gene sequencing showed that the bacterial richness was significantly reduced, and the rumen bacterial composition was significantly altered with the increasing levels of dietary energy and protein. Metabolomics analysis revealed that the dominant differential metabolites were amino acids, peptides, and analogs. Moreover, high-energy and high-protein diets could enhance the ruminal antioxidative capacity by increasing the concentration of some metabolites. Correlation analysis implied that high energy and protein levels could enhance the catechol concentration by Prevotella_1 and Ruminococcus_2. This study can help to improve the dietary energy and protein use efficiency in goats. ABSTRACT: This study was conducted to investigate the impacts of dietary energy and protein on rumen bacterial composition and ruminal metabolites. A total of 12 ruminal samples were collected from Shaanbei white cashmere goats which were divided into two groups, including high-energy and high-protein (Group H; crude protein, CP: 9.37% in dry matter; metabolic energy, ME: 9.24 MJ/kg) and control (Group C; CP: 8.73%; ME: 8.60 MJ/kg) groups. Thereby, 16S rRNA gene sequencing and a quantitative polymerase chain reaction were performed to identify the rumen bacterial community. Metabolomics analysis was done to investigate the rumen metabolites and the related metabolic pathways in Groups C and H. The high-energy and high-protein diets increased the relative abundance of phylum Bacteroidetes and genera Prevotella_1 and Succiniclasticum, while decreasing the number of Proteobacteria (p < 0.05). The dominant differential metabolites were amino acids, peptides, and analogs. Tyrosine metabolism played an important role among the nine main metabolic pathways. Correlation analysis revealed that both Prevotella_1 (r = 0.608, p < 0.05) and Ruminococcus_2 (r = 0.613, p < 0.05) showed a positive correlation with catechol. Our findings revealed that the diets with high energy and protein levels in Group H significantly altered the composition of ruminal bacteria and metabolites, which can help to improve the dietary energy and protein use efficiency in goats.