Total milk solid (TMS) content directly reflects the quality of milk. Rumen bacteria ferment dietary components, the process of which generates the precursors for the synthesis of milk solid, therefore, the variation in rumen bacterial community could be associated with milk solid in dairy cows. In this study, 45 healthy mid-lactation Holstein dairy cows with the similar body weight, lactation stage, and milk yield were initially used for the selection of 10 cows with high TMS (HS) and 10 cows with low TMS (LS). All those animals were under the same feeding management, and the individual milk yield was recorded for 14 consecutive days before milk and rumen fluid were sampled. Rumen fluid was used to determine bacterial community by 16S rRNA gene sequencing technique. The HS cows had significantly greater feed intake and milk TMS, fat, protein content than LS cows (P < 0.05). Among the volatile fatty acids (VFA), propionic acid and valeric acid concentrations were significantly greater in HS cows than those in LS cows (P < 0.05). There was no significant difference in the concentrations of acetate, butyrate, isobutyrate, valerate, and the total VFA (P > 0.05), nor was the acetate-to-propionate ratio, pH value, ammonia nitrogen and microbial crude protein concentrations (P > 0.05). Significant differences in the relative abundances of some bacterial genera were found between HS and LS cows. Spearman’s rank correlation analysis revealed that TMS content was correlated positively with the abundances of Ruminococcaceae UCG-014, Ruminococcaceae NK4A214 group, Prevotellaceae UCG-001, Butyrivibrio 2, Prevotellaceae UCG-003, Candidatus Saccharimonas, Ruminococcus 2, Lachnospiraceae XPB1014 group, probable genus 10, Eubacterium ventriosum group, but negatively correlated with Pyramidobacte. In addition, Ruminococcaceae UCG-014, Ruminococcus 2, Ruminococcaceae UCG001, probable genus 10 and Eubacterium ventriosum group might boost the total VFA production in the rumen. In conclusion, the dry matter intake of dairy cows and some special bacteria in rumen were significantly associated with TMS content, which suggests the potential function of rumen bacteria contributing to TMS content in dairy cows.

总乳固体（TMS）含量直接反映了牛奶的质量。瘤胃细菌发酵日粮成分，该过程产生乳固体合成的前体，因此，瘤胃细菌群落的变化可能与奶牛的乳固体有关。在这项研究中，最初使用 45 头具有相似体重、泌乳期和产奶量的健康的泌乳中期荷斯坦奶牛来选择 10 头 TMS（HS）高的奶牛和 10 头 TMS（LS）低的奶牛。所有这些动物都在相同的饲养管理下，连续14天记录个体产奶量，然后对牛奶和瘤胃液进行取样。瘤胃液通过16S rRNA基因测序技术确定细菌群落。HS 奶牛的采食量和牛奶 TMS、脂肪、P < 0.05)。在挥发性脂肪酸（VFA）中，HS奶牛的丙酸和戊酸浓度显着高于LS奶牛（P < 0.05）。乙酸、丁酸、异丁酸、戊酸和总 VFA 浓度差异无统计学意义（P > 0.05），乙酸丙酸比、pH 值、氨氮和微生物粗蛋白浓度均无显着性差异（P > 0.05)。在 HS 和 LS 奶牛之间发现了一些细菌属的相对丰度存在显着差异。Spearman秩相关分析显示TMS含量与瘤胃球菌科UCG-014、瘤胃球菌科NK4A214组、Prevotellaceae UCG-001, Butyrivibrio 2 , Prevotellaceae UCG-003, Candidatus Saccharimonas , Ruminococcus 2, Lachnospiraceae XPB1014 group, probable genus 10, Eubacterium v​​entriosum group, 但与Pyramidobacte呈负相关。此外，瘤胃球菌科UCG-014、瘤胃球菌2、瘤胃球菌科UCG001、可能属 10 和Eubacterium v ​​entriosum组可能会提高瘤胃中 VFA 的总产量。总之，奶牛的干物质摄入量和瘤胃中的一些特殊细菌与 TMS 含量显着相关，这表明瘤胃细菌对奶牛 TMS 含量的潜在作用。