Effect of STAT5A Gene Polymorphism on Milk Production Traits in Iranian Holstein Bulls

Signal transducer and activator of transcription 5A (STAT5A) was chosen as candidategene because of its involvement in the development of the mammary gland and it is a keymediator of prolactin signaling and can activate transcription of milk protein genes in response to prolactin. Semen samples from 134 Iranian Holstein proven bulls were obtained from the Animal Breeding Center of Iran. A 215 bp fragment, located within exon 7 of bovine STAT5A gene was amplified. PCR product was digested with AvaI enzyme. Genotypic frequencies of CC and TC were 0.739 and 0.261 respectively and gene frequencies of T and C alleles were 0.131 and 0.869 respectively. Genotypes are distributed according to the Hardy-Weinberg equilibrium. Breeding values for milk related traits (milk, fat and protein yield and percent age) were estimated using animal model and AIREML procedures as programmed in MATVEC software. Least squares means between two genotypes for protein yield were significance (P<0.016) and TC genotype had higher protein yield. We can conclude that RFLP in STAT5A is a promising new possibility to select for increased yield of milk protein through selection for the T allele.