The study of candidate genes, based on physiological effects, is an important tool to identify genes to be used in marker-assisted selection programs. On the basis of sheep genome mapping information the ovine GHR and GHRHR genes was examined as a possible genetic marker for growth traits in sheep. Evaluation of the genetic diversity for 2 genes in 102 animals of the Iranian indigenous sheep breed (Ovis Aries) Baluchi was done. The genotypes for GHR and GHRHR loci were determined by the PCR-SSCP method. Single-nucleotide Polymorphisms (SNP) (Exon10) were discovered in the Growth Hormone Receptor (GHR) gene but Growth Hormone Releasing Hormone Receptor (GHRH-R) was monomorphic. Moreover, associations were studied between the polymorphism at GH Receptor (GHR) loci and growth trait in the growing Baluchi sheep. The traits analyzed were Birth Weight (BW), Average daily Gain from Birth to Weaning (GBW), weaning to 6 month (GWS) and from 6 month to Yearling Age (GSY). In the association studies, traits of interest were analyzed using the General Linear Model (GLM) procedure of the SAS program and least squares means of the genotypes were compared by the Tukey test. Only significant associations (p<0.05) were observed between the genotype of the GHR polymorphism and Average daily Gain from Birth to Weaning (GBW). These results confirmed the potential usefulness of GHR gene in marker-assisted selection programs for sheep breeding.

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