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.