1. Potential Role of Lauric Acid in Milk Fat Synthesis in Chinese Holstein Cows Based on Integrated Analysis of Ruminal Microbiome and Metabolome.
- Author
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Zhang, Huimin, Wang, Yi, Hu, Liping, Cong, Jiahe, Xu, Zhengzhong, Chen, Xiang, Rao, Shengqi, Li, Mingxun, Shen, Ziliang, Mauck, John, Loor, Juan J., Yang, Zhangping, and Mao, Yongjiang
- Subjects
MILKFAT ,LIQUID chromatography-mass spectrometry ,LAURIC acid ,MILK proteins ,FAT ,FAT content of milk ,COWS - Abstract
Simple Summary: Milk fat is one of the most important economic traits in dairy cow production. Numerous investigations have demonstrated the influence of the ruminal microbiome's composition and metabolic profile on milk production. However, no studies have directly connected the ruminal metabolome with bacterial and fungal communities as a function of milk fat content in dairy cows. The specific objective of the present study was to compare ruminal metabolome with bacterial and fungal communities among Chinese Holstein cows with contrasting milk fat content that were fed the same diet. Our results confirm that ruminal metabolome, bacterial, and fungal communities differ significantly in dairy cows with different milk fat contents. Among these different metabolites, lauric acid was enriched in fatty acid biosynthesis and selected for an in vitro study with bovine mammary epithelial cells, indicating that lauric acid promoted intracellular triglyceride synthesis via upregulation of the mRNA abundance of fatty acid uptake and activation, as well as lipogenesis. This study revealed microbial-mediated metabolic processes related to milk fat synthesis. The composition and metabolic profile of the ruminal microbiome have an impact on milk composition. To unravel the ruminal microbiome and metabolome affecting milk fat synthesis in dairy cows, 16S rRNA and internal transcribed spacer (ITS) gene sequencing, as well as ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS/MS) methods were used to investigate the significant differences in ruminal bacterial and fungal communities as well as metabolome among Chinese Holstein cows with contrasting milk fat contents under the same diet (H-MF 5.82 ± 0.41% vs. L-MF 3.60 ± 0.12%). Another objective was to culture bovine mammary epithelial cells (BMECs) to assess the effect of metabolites on lipid metabolism. Results showed that the acetate-to-propionate ratio and xylanase activity in ruminal fluid were both higher in H-MF. Microbiome sequencing identified 10 types of bacteria and four types of fungi differently abundant at the genus level. Metabolomics analysis indicated 11 different ruminal metabolites between the two groups, the majority of which were lipids and organic acids. Among these, lauric acid (LA) was enriched in fatty acid biosynthesis with its concentration in milk fat of H-MF cows being greater (217 vs. 156 mg per 100 g milk), thus, it was selected for an in vitro study with BMECs. Exogenous LA led to a marked increase in intracellular triglyceride (TG) content and lipid droplet formation, and it upregulated the mRNA abundance of fatty acid uptake and activation (CD36 and ACSL1), TG synthesis (DGAT1, DGAT2 and GPAM), and transcriptional regulation (SREBP1) genes. Taken together, the greater relative abundance of xylan-fermenting bacteria and fungi, and lower abundance of bacteria suppressing short-chain fatty acid-producing bacteria or participating in fatty acid hydrogenation altered lipids and organic acids in the rumen of dairy cows. In BMECs, LA altered the expression of genes involved in lipid metabolism in mammary cells, ultimately promoting milk fat synthesis. Thus, it appears that this fatty acid plays a key role in milk fat synthesis. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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