This study aimed to evaluate the effects of partial reducing rumen-protected Lys (RPLys) on rumen fermentation and microbial composition in heifers. Three ruminal fistulated Holstein Friesian bulls were used to determine the effective degradability of RPLys using an in situ method at incubation times of 0, 2, 6, 12, 16, 24, 36, and 48 h. Thereafter, 36 Holstein heifers at 90 days of age were assigned to one of two dietary treatments: a theoretically balanced amino acid diet (PC group; 1.21% Lys, 0.4% Met) or a 30% Lys-reduced diet (PCLys group, 0.85% Lys, 0.4% Met). Rumen fluid samples from five heifers in each group were extracted using esophageal tubing on day 90 to determine pH, microprotein, ammonia, volatile fatty acids, and microbial communities. Results showed that the effective ruminal degradability was 25.76%. Furthermore, differences in rumen fermentation parameters and alpha diversity of the microbiota between the two groups were not significant, but beta diversity was significant. Based upon relative abundance analysis, short-chain fatty acid–producing bacteria, including Sharpea, Syntrophococcus, [Ruminococcus]_gauvreauii_group, Acetitomaculum, and [Eubacterium]_nadotum_group belonging to Firmicutes, were significantly decreased in the PCLys group. Spearman’s analysis revealed a positive correlation between the butyrate molar proportion and the relative abundance of butyrate-producing bacteria such as [Eubacterium]_nadotum_group, Coprococcus_1, Ruminococcaceae_UCG_013, Pseudoramibacter, and Lachnospiraceae_UCG_010. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States analysis further validated that RPLys deduction influenced energy metabolism. Together, our findings highlight the role of RPLys or Lys in butyrate-producing bacteria. However, the number of bacteria affected by Lys was very limited and insufficient to alter rumen fermentation.

这项研究旨在评估部分还原瘤胃保护的赖氨酸（RPLys）对小母牛瘤胃发酵和微生物组成的影响。使用三只瘤胃瘘的霍尔斯坦弗里斯兰公牛在0、2、6、12、16、16、24、36和48 h的孵育时间使用原位方法确定RPLys的有效降解能力。此后，将90天龄的36头荷斯坦牛指定为两种饮食疗法之一：理论上均衡的氨基酸饮食（PC组； 1.21％Lys，0.4％Met）或30％降低Lys饮食（PCLys组，0.85） ％Lys，0.4％Met）。在第90天，使用食管从每组五个小母牛的瘤胃液样品中提取样品，以测定pH，微蛋白，氨，挥发性脂肪酸和微生物群落。结果显示有效瘤胃降解率为25.76％。此外，两组之间的瘤胃发酵参数和微生物群的α多样性差异不显着，但β多样性显着。根据相对丰度分析，产生短链脂肪酸的细菌包括Sharpea，Syntrophococcus，[瘤胃球菌] _gauvreauii_group，Acetitomaculum，和[真杆菌] _nadotum_group属于硬壁菌门，所述PCLys组中显著下降。斯皮尔曼的分析表明丁酸摩尔比例和丁酸产生菌如的相对丰度之间的正相关[真杆菌] _nadotum_group，Coprococcus_1，Ruminococcaceae_UCG_013，Pseudoramibacter和Lachnospiraceae_UCG_010。通过重建未观察到的国家进行的系统进化研究进一步证实了RPLys的减少会影响能量代谢。在一起，我们的发现突出了RPLys或Lys在产生丁酸盐的细菌中的作用。但是，受Lys影响的细菌数量非常有限，不足以改变瘤胃发酵。