The Biological Properties of the FAS and TACR3 Genes and the Association of Single-Nucleotide Polymorphisms with Milk Quality Traits in Gannan Yak

Fatty acid synthase (<i>FAS</i>) is a fundamental metabolic enzyme that catalyzes the synthesis of endogenous fatty acids; TACR3, also known as tachykinin receptor 3 or NK3R, is an important G-protein-coupled receptor that is primarily responsible for responding to neuropeptides such as neurokinin B (NKB) and plays a crucial role in embryonic development, organ formation, and cell differentiation. This study aimed to explore the association between the single-nucleotide polymorphisms (SNPs) of the <i>FAS</i> and <i>TACR3</i> genes and the milk quality of Gannan yak and to determine them as potential molecular marker loci for the milk quality of yaks. The genotyping of 162 Gannan yaks was performed using liquid-phase chip technology. Association analyses were conducted between the obtained SNP loci genotypes and milk composition traits, including milk protein, casein, non-fat solids, and acidity. Comparative sequence analysis of two genes (<i>FAS</i> and <i>TACR3</i>) across multiple species revealed that the yak <i>FAS</i> gene exhibited the highest homology with <i>Bos taurus</i> and <i>Bos indicus</i>, while the yak <i>TACR3</i> gene showed the greatest sequence similarity to <i>Bos taurus</i>. Hardy-Weinberg equilibrium tests were performed on four SNP loci, and the equilibrium indices of the four loci were 0.799, 0.368, 0.689, and 0.948 (<i>p</i> > 0.05), indicating that all of these loci are in Hardy-Weinberg equilibrium state. g.13,276T>C (<i>FAS</i>) was significantly correlated with lactose content traits (<i>p</i> < 0.05); g.74,382C>G (<i>FAS</i>) was significantly correlated with casein, protein, total solids, non-fat solids, and acidity traits (<i>p</i> < 0.05); g.40,529A>G (<i>TACR3</i>) was significantly correlated with protein, non-fat solids, citric acid, and acidity traits (<i>p</i> < 0.05). The influence of g.40,555C>T (<i>TACR3</i>) on these traits did not reach a significant level (<i>p</i> > 0.05). This study suggests that two genes can serve as potential candidate genes affecting the quality of Gannan yak milk, providing reference genes for improving the quality of Gannan yak milk.