Association of genetic variants in STAT5B gene with milk performance and mastitis related traits in dairy cattle

Udder performance and health are important traits in dairy cattle worldwide. The present study aimed to explore the association of single nucleotide polymorphisms (SNPs) in the STAT5B gene in dairy cattle with milk performance and mastitis related traits. The study included 201 cows of three pure breeds (i.e. Holstein Friesian, Jersey and Achai) and two crossbred cattle at four established dairy farms in Khyber Pakhtunkhwa, Pakistan. The milk samples were analysed for somatic cell count (SCC) and milk composition (i.e. fat, protein and lactose percentages). The generalized linear model was deployed for association analysis using SAS. The pool DNA sequencing showed four (three synonymous and a 3/ UTR) SNPs in STAT5B. These SNPs were further validated in all DNA samples using SNaPshot assay. The breed-wise analysis showed that most of the SNPs were consistent with Hardy-Weinberg equilibrium (P>0.05). The association analysis revealed a significantly higher protein percentage in TT genotype and lower SCC in CC genotypes of SNP 1 (exon 2, C>T), whereas in SNP 2 (exon 16, T>C) the TT genotypes revealed significantly lower SCC and SCS compared with other genotypes (P<0.05). SNP 4 (3(/) UTR, C>T) showed significantly lower SCC and frequency of clinical mastitis in the heterozygous (CT) genotype compared to the homozygous genotypes. The in silico predictions revealed changes in the RNA secondary structure for SNP 2 and SNP 3. The study suggests that STAT5B should be considered as a candidate gene, and the variants identified as useful genetic markers for improved milk composition and udder health.