Effects of bovine prolactin gene polymorphism within exon 4 on milk related traits and genetic trends in Iranian Holstein bulls

In this study, polymorphism of prolactin gene was analyzed as a candidate gene responsible for variation and genetic trends in milk yield and composition traits. Genomic DNAs were extracted from 268 semen samples belonged to Iranian Holstein bulls. Genotyping for the prolactin gene using PCR-RFLP technique and Rsal restriction endonuclease showed a mutation in 294-bp fragment located in exon 4. The frequencies of A and G alleles were 0.069 and 0.931, respectively. The allelic substitution effect was significant for milk and protein yield (p < 0.05). The G allele was unfavorable for milk and protein yield. Genetic trends for all analyzed traits were significant (p < 0.01) and that was progressive for milk, fat and protein yield, but diminishing for fat and protein percent. The effects of prolactin SNP on genetic trends and the difference between genetic trends produced by A and G alleles were not significant for all studied traits.