Table_2_Metagenomic and Metabolomic Insights Into the Mechanism Underlying the Disparity in Milk Yield of Holstein Cows.XLSX

This study was conducted to investigate the metabolic mechanism underlying the disparity in the milk yield of Holstein cows. Eighteen lactating Holstein cows in their second parity and 56 (±14.81 SD) days in milking (DIM) were selected from 94 cows. Based on the milk yield of the cows, they were divided into two groups of nine cows each, the high milk yield group (HP) (44.57 ± 2.11 kg/day) and the low milk yield group (LP) (26.71 ± 0.70 kg/day). The experimental cows were fed the same diet and kept under the same management system for more than 60 days. Rumen metagenomics revealed that two Archaea genera, one Bacteria genus, eight Eukaryota genera, and two Virus genera differ between the HP and LP groups. The analysis of metabolites in the rumen fluid, milk, and serum showed that several metabolites differed between the HP and LP groups. Correlation analysis between the predominant microbiota and milk yield-associated metabolites (MP-metabolites) revealed that four Bacteria and two Eukaryota genera have a positive relationship with MP-metabolites. Pathway enrichment analysis of the differential metabolites revealed that five pathways were enriched in all the samples (two pathways in the milk, two pathways in the serum, and one pathway in the rumen fluid). Further investigation revealed that the low milk yield observed in the LP group might be due to an upregulation in dopamine levels in the rumen fluid and milk, which could inhibit the release of prolactin or suppress the action of oxytocin in the udder resulting in reduced milk yield. On the other hand, the high milk yield in the HP group is attributed to an upregulation in citrulline, and N-acetylornithine, which could be used as substrates for energy metabolism in the citric acid cycle and ultimately gluconeogenesis.

本研究旨在探究荷斯坦奶牛产奶量差异背后的代谢机制。从94头奶牛中选取18头处于第二泌乳期、泌乳天数（Days in Milking, DIM）为56±14.81的泌乳荷斯坦奶牛。根据奶牛产奶量将其分为两组，每组各9头：高产奶量组（HP，44.57±2.11 kg/天）与低产奶量组（LP，26.71±0.70 kg/天）。实验奶牛饲喂相同日粮，在统一管理体系下饲养超过60天。
瘤胃宏基因组学（rumen metagenomics）分析显示，高产组与低产组间存在2个古菌属（Archaea genera）、1个细菌属（Bacteria genus）、8个真核生物属（Eukaryota genera）以及2个病毒属（Virus genera）的菌群差异。对瘤胃液、乳汁与血清中的代谢物进行分析发现，两组间存在多种差异代谢物。对优势菌群与产奶量相关代谢物（MP-metabolites）开展相关性分析，结果显示4个细菌属和2个真核生物属与MP-metabolites呈正相关。差异代谢物的通路富集分析表明，所有样本中共富集到5条通路：乳汁中2条、血清中2条、瘤胃液中1条。
进一步研究发现，低产组的低产奶量可能源于瘤胃液与乳汁中多巴胺水平上调，该变化可抑制催乳素释放，或抑制催产素在乳腺中的作用，最终导致产奶量降低。另一方面，高产组的高产奶量则归因于瓜氨酸（citrulline）与N-乙酰鸟氨酸（N-acetylornithine）的表达上调，这两种物质可作为柠檬酸循环能量代谢的底物，最终参与糖异生过程。