Effects of different models of feeding and management and concentrate-to-forage ratios on the structure and function of rumen microbiota in yaks in the cold season

Twenty-four male yaks (Bos grunmiens) at the age of 24 months with similar body weights and good body conditions were randomly divided into four groups. The RCG1 group was grazed naturally in a winter pasture, and the RCC90, RCC70, and RCC50 groups were fed diets with concentrate-to-forage ratios of 90 ꞉ 10, 70 ꞉ 30, and 50 ꞉ 50, respectively. The rumen fluid of each group was collected at the end of the experiment, and the bacterial community structure was detected using 16S rDNA sequencing, The data were analyzed, and the bacterial function were performed; the aim of this study was to investigate the effect of feeding management patterns and dietary concentrate to forage ratios on the composition, diversity, and function of rumen microbiota in yaks. A total of 20 696 ASVs were detected in 24 samples, and 4 966, 3 069, 3 680, and 3 536 ASVs were specifically expressed in RCG1, RCC90, RCC70, and RCC50 yaks, respectively. At the phylum and genus levels, the dominant bacteria in the samples from the four groups were Firmicutes, Bacteroidota and Proteobacteria at the phylum level, and Rikenellaceae_RC9_gut_group, Prevotella, Christensenellaceae_R-7_group at the genus level. There were significant differences in the rumen microbiota composition and abundance between the RCG1 and supplemented groups (P < 0.05). The Firmicutes/Bacteroidetes (F/B) ratio of each supplemented group was significantly higher than that of the RCG1 group (P < 0.05). Compared to the RCG1 group, Rikenellaceae_RC9_gut_group, Anaerovorax and Lachnospiraceae_UCG-009 were significantly downregulated (P < 0.05) in the RCC50, RCC70, and RCC90 groups, whereas Prevotella, Ferruginibacter and Clostridia_UCG-014 were significantly upregulated (P < 0.05) in the RCC50, RCC70, and RCC90 groups. In addition, the differences in rumen microbiota function among the four groups were not significant (P > 0.05) and were mainly annotated as biological processes such as nutrient metabolism, replication, and repair. Feeding management patterns and dietary concentrate-to-forage ratios significantly affected rumen microbiota structure (P < 0.05) but not function. The rumen microbiota abundance and diversity of yaks were significantly improved by 10% concentrate supplementation in the cold season (P < 0.05), and the rumen microbiota was the best for feed digestion and absorption when supplemented with 30% high-protein concentrate.