Macrogenomics-based analysis of rumen microbial composition and their metabolic pathways in yaks under different dietary concentrate-to-forage ratios

This study aimed to investigate the regulatory mechanisms underlying feed efficiency(FE) in yaks by analyzing the composition of rumen microorganisms and their major metabolic pathways using metagenomic analysis under different dietary concentrate-to-forage ratios. A total of 40 Qinghai Plateau yaks (8–9months old) with similar body weights (68.725±18.973kg)were randomly assigned to four treatment groups (n=10per group).The experimental groups were fed diets with concentrate-to-forage ratios of 80:20 (C80), 65:35 (C65), 50:50 (C50), and 35:65 (C35), respectively. The study included a 15-day pre-feeding period followed by a 105-day experimental feeding period.The results indicated that the total weight gain in the C65 group was significantly higher than in the C50 and C35 groups by 29.91% and 28.97%, respectively (P<0.05). Additionally, the rumen pH in the C80 group was significantly higher than in the C65, C50, and C35 groups (P<0.05). Metagenomic analysis revealed significant differences (P<0.05) in bacterial and archaeal community compositions across groups. Bacteroidota, Bacillota, Prevotella, Bacteroides, and Ruminococcus were identified as the dominant bacterial taxa at the phylum and genus levels. Functional analysis of rumen microbial metabolism showed that in the C35 group, pathways related to starch and sucrose metabolism, as well as fructose and mannose metabolism, were significantly different from those in other groups. The C35 group exhibited higher activity in functional pathways related to starch and sucrose metabolism, fructose and mannose metabolism, cellulose degradation, and methanolysis. In contrast, the C80 group showed greater activity in cellulose degradation and methane metabolism. Notably, the C65 group exhibited the highest activity in sugar metabolism pathways (ko00500), facilitating starch and soluble sugar degradation and the rapid conversion of pyruvic acid into acetic acid and propionate. This enhanced energy utilization efficiency, suggesting a superior capacity for sugar metabolism.In conclusion, the dietary composition of the C65 group demonstrated the most favorable effects on growth performance, rumen fermentation optimization, and microbial balance maintenance.本研究旨在通过宏基因组分析（metagenomic analysis），探究不同精粗比条件下青海高原牦牛的瘤胃微生物组成及其主要代谢通路，以解析其饲料效率（Feed Efficiency, FE）的调控机制。共计纳入40头8~9月龄、初始体重为68.725±18.973kg的青海高原牦牛，随机分为4个处理组（每组n=10）。各试验组分别饲喂精粗比为80:20（C80）、65:35（C65）、50:50（C50）及35:65（C35）的日粮。试验设置15天预饲期与105天正式饲喂期。结果显示，C65组总增重显著高于C50与C35组，分别提升29.91%与28.97%（P<0.05）。此外，C80组瘤胃pH显著高于C65、C50及C35组（P<0.05）。宏基因组分析表明，各组间细菌与古菌群落组成存在显著差异（P<0.05）。在门和属水平上，拟杆菌门（Bacteroidota）、厚壁菌门（Bacillota）、普雷沃氏菌属（Prevotella）、拟杆菌属（Bacteroides）及瘤胃球菌属（Ruminococcus）被鉴定为优势菌群。瘤胃微生物代谢功能分析显示，C35组的淀粉与蔗糖代谢、果糖与甘露糖代谢通路与其他组存在显著差异。C35组在淀粉与蔗糖代谢、果糖与甘露糖代谢、纤维素降解及甲醇解相关功能通路中活性更高。与之相反，C80组在纤维素降解与甲烷代谢通路中活性更强。值得注意的是，C65组在糖代谢通路（ko00500）中活性最高，可促进淀粉与可溶性糖降解，并将丙酮酸快速转化为乙酸与丙酸，提升能量利用效率，提示其具备更优异的糖代谢能力。综上，C65组日粮组成对牦牛生长性能、瘤胃发酵优化及微生物平衡维持均展现出最优效果。