Effects of Genetic Polymorphism in the <i>IFI27</i> Gene on Milk Fat Traits and Relevance to Lipid Metabolism in Bovine Mammary Epithelial Cells

Milk fat is an important indicator for evaluating milk quality and a symbol of the core competitiveness of the dairy industry. It can be improved through genetic and feed management factors. Interferon alpha-inducible protein 27 (<i>IFI27</i>) was found to be differentially expressed when comparing the transcriptome in high- and low-fat bovine mammary epithelial cells (bMECs) in our previous research. Therefore, this study aimed to investigate whether the IFI27 gene had a regulatory effect on lipid metabolism.We detected six SNPs in the <i>IFI27</i> gene (UTR-(-127) C>A, UTR-(-105) T>A, UTR-(-87) G>A, I1-763 G>T, E2-77 G>A, E2-127 G>T) in a Chinese Holstein cow population. Association analysis of the polymorphism of <i>IFI27</i> and milk quality traits showed that the AG and GG genotype of E2-77 G>A, and the GG and TT genotypes of E2-127 G>T were connected to milk fat (<i>p</i> < 0.05). Haplotype frequency analysis showed that H5H5 was associated with lower milk fat content (<i>p</i> < 0.05), while milk from H5H6 animals had a higher fat content (<i>p</i> < 0.05). Subsequently, <i>IFI27</i> overexpression vectors (PBI-CMV3-<i>IFI27</i>) and interference vectors (Pb7sk-GFP-shRNA) were constructed. Overexpression of the <i>IFI27</i> gene in bMECs caused a significant increase in triglycerides (TGs) content (<i>p</i> < 0.05) and decreases in cholesterol (CHOL) and nonestesterified fatty acid (NEFA) content (<i>p</i> < 0.05), while interference with <i>IFI27</i> expression produced opposing changes (<i>p</i> < 0.05). In summary, <i>IFI27</i> E2-77 G>A and <i>IFI27</i> E2-127 G>T may be useful as molecular markers in dairy cattle to measure milk fat, and the <i>IFI27</i> gene may play an important role in milk lipid metabolism.