Identification of Genetic Associations of , , and Genes with Milk Yield and Compositions in Dairy Cows.

Previous study revealed that isocitrate dehydrogenase (NADP (+)) 2, mitochondrial (), lactate dehydrogenase A (), and lactate dehydrogenase B () genes were significantly differentially expressed in liver tissues of Holstein cows among different lactation periods and associated with lipid and protein metabolism; hence, they were considered as candidates for milk production traits. Herein, the genetic effects of the three genes on milk yield, fat, and protein traits were studied by association analysis using 926 Chinese Holstein cows from 45 sire families. As a result, five single nucleotide polymorphisms (SNPs) in , one in , and three in were identified by re-sequencing, and subsequently, they were genotyped in 926 Chinese Holstein cows by genotyping by target sequencing (GBTS). With the animal model, single-locus association analysis revealed that four SNPs in and one SNP in were significantly associated with milk, fat, and protein yields ( ≤ 0.0491), and three SNPs in were associated with milk yield, milk fat yield, and fat percentage ( ≤ 0.0285). Further, four IDH2 SNPs were found to form a haplotype block significantly associated with milk yield, fat yield, protein yield, and protein percentage ( ≤ 0.0249). In addition, functional predictions indicated that one SNP in , g.26304153G>A, may affect transcription factor binding and two SNPs, g.88544541A>G and g.88556310T>C could alter mRNA secondary structure. In summary, this study profiled the significant genetic effects of , , and on milk yield and composition traits and provided referable genetic markers for genomic selection programs in dairy cattle.