Effects of Dietary Concentrate-to-Roughage Ratio on Rumen Microbial Community Structure, Functional Potential, and Fermentation Factors: A Metagenomic Sequencing Analysis

This study investigated the effects of different concentrate-to-roughage ratios on the rumen microbial community, functional potential, and fermentation characteristics in yak. Results: Forty Qinghai plateau-type yaks of similar age (8–9 months) and body weight (68.725 ± 18.973 kg) were randomly assigned to four treatment groups, with 10 replicates per group. The diets had concentrate-to-roughage ratios of 80:20 (C80), 65:35 (C65), 50:50 (C50), and 35:65 (C35), respectively. Following a 15-day pre-feeding period, animals were subjected to a 105-day main feeding period. Rumen contents were analyzed using metagenomic sequencing combined with measurements of physicochemical fermentation parameters.
Conclusions:Beta diversity analysis showed that high-concentrate diets (C80 and C65) enriched starch-degrading and propionate-producing bacteria, such as Prevotella and Succiniclasticum, whereas low-concentrate diets (C50 and C35) favored cellulolytic bacteria, including Ruminococcus and Fibrobacter. Functional annotation indicated that increasing the concentrate proportion significantly enhanced pathways related to glycolysis (ko00010), propanoic acid metabolism (ko00640), and energy production, while low-concentrate diets maintained enrichment of fiber degradation and methane metabolism pathways. Rumen fermentation characteristics were consistent with these microbial shifts: pH decreased significantly with increasing concentrate levels (P = 0.001), and NH₃-N concentrations differed among treatment groups (P = 0.036). High-concentrate feeding promoted rapid carbohydrate fermentation and propionic acid production, whereas roughage-dominant diets maintained higher pH and acetate dominance. In summary, the concentrate-to-roughage ratio plays a pivotal role in modulating rumen microbial ecology and metabolic activity. A moderate ratio (approximately 65:35) provides an optimal balance between energy utilization efficiency and rumen environmental stability, offering a theoretical basis for improving feed conversion efficiency and supporting sustainable yak production on the Qinghai–Tibet Plateau.