The effects of different dietary energy levels on the ruminal bacterial population, selected meat quality indices, and their relationship in yak longissimus thoracis (LT) muscle were assessed in this study. A total of 15 castrated yaks were randomly assigned to three groups with low- (NEg: 5.5 MJ/Kg, LE), medium- (NEg: 6.2 MJ/Kg, ME), and high- (NEg: 6.9 MJ/Kg, HE) dietary energy levels and occurred in the cold season (March to May). All yaks from each treatment group were humanely slaughtered and sampled on the day of completion of their feeding treatment. The results showed that the water content and crude fat levels of the LT muscle were markedly elevated in the HE group (P < 0.05), while the shear force was drastically reduced (P = 0.001). Methionine, aspartic acid, and glycine levels in the LT muscle were higher in the LE group compared with the ME and HE groups (P < 0.05). The glutamic acid level in the ME group was greater in comparison to the LE and HE groups (P < 0.05), while the histidine level in the ME group was higher than that in the HE group (P < 0.05). Additionally, the HE diet significantly elevated (P < 0.05) the abundance of carbohydrate metabolism-associated bacteria including Prevotella_1, Lachnospiraceae_NK4A136_group, U29_B03, Ruminiclostridium_6, and Ruminococcaceae_UCG_013 in the rumen. The results of the Spearman's rank correlation analysis showed that the abundance of uncultured_bacterium_f_vadinBE97 and uncultured_bacterium_f_Lachnospiraceae showed a significant influence on the indicator of IMF and SF. In conclusion, a high dietary energy level improved the meat quality in the LT muscle of yak mainly by increasing the relative abundance of ruminal amylolytic bacteria to provide substrates for fatty acid synthesis.

不同日粮能量水平对牦牛瘤胃细菌数量、选定肉质指标的影响及其相互关系 胸最长肌(LT) 肌肉在这项研究中进行了评估。总共 15 头去势牦牛被随机分配到低（NEg：5.5 MJ/Kg，LE）、中（NEg：6.2 MJ/Kg，ME）和高（NEg：6.9 MJ/Kg， HE) 膳食能量水平，发生在寒冷季节（3 月至 5 月）。每个处理组的所有牦牛都在完成饲养处理当天进行人道屠宰和取样。结果显示，HE组LT肌肉的水分含量和粗脂肪水平显着升高（磷 < 0.05)，而剪切力显着降低 (磷= 0.001）。与 ME 和 HE 组相比，LE 组 LT 肌肉中的蛋氨酸、天冬氨酸和甘氨酸水平更高。磷< 0.05)。与 LE 和 HE 组相比，ME 组的谷氨酸水平更高（磷 < 0.05），而ME组组氨酸水平高于HE组（磷< 0.05)。此外，HE饮食显着升高（磷 < 0.05) 碳水化合物代谢相关细菌的丰度，包括 Prevotella_1、毛螺菌科_NK4A136_group、U29_B03、瘤胃梭菌_6和瘤胃球菌科_UCG_013在瘤胃中。Spearman 秩相关分析结果表明，uncultured_bacterium_f_vadinBE97 和 uncultured_bacterium_f_Lachnospiraceae对IMF和SF指标有显着影响。总之，高日粮能量水平主要通过增加瘤胃淀粉分解菌的相对丰度来改善牦牛LT肌肉的肉质，从而为脂肪酸合成提供底物。