association of tg-repeats in the 5’-flanking region of bovine growth hormone receptor (ghr) gene with milk production traits and somatic cell count in holstein cattle

the growth hormone receptor (ghr) is a member of cytokine/hematopoietin family that mediates the biological actions of growth hormone (gh) on target tissues. therefore, the purpose of this study was to examine the association of tg-repeat polymorphisms in the 5’-flanking region of bovine ghr gene with milk production traits and somatic cell score (scs) in holstein cattle of iran. the part of 5’-flanking region of ghr gene that encompassed tg-repeat was screened by single strand conformation polymorphism (sscp) method and dna sequencing. five hundred eighteen iranian holstein cows were genotyped, giving 3 distinct sscp patterns (a, b, and c). frequencies of these patterns for the amplified fragment were 0.21, 0.26 and 0.53, respectively. statistical analysis revealed that tg-repeat had a significant effect on average daily milk production (p < 0.05) and tended to associate with fat and protein percentage. no significant difference was observed between tg-genotypes and scs. the association identified in the tg-repeat of ghr gene may have potential to serve as candidate genetic marker for marker assisted selection (mas) in cattle.