This investigation aimed to study polymorphism of growth hormone (GH), growth hormone receptor (GHR), and insulin like growth factor 1 (IGF - 1 ) genes and their associations with growth and carcass traits in Mazandaran native chicken. 200 male chicks were reared and slaughtered at 12 weeks of age. Traits including live weight at 4 , 8 and 12 weeks of age, body weight and weights of heart, liver, gizzard, spleen, and abdominal fat, pH of meat, water holding capacity of the meat and intramuscular fat were recorded. Before dissecting birds, blood samples were collected and DNA was extracted. The frequency of alleles (+ and - ) were determined t o be 0.627 and 0.373 for GH locus, 0.715 and 0.285 for GHR locus, and 0.407 and 0.593 for IGF - 1 gene locus, respectively. Hardy - Weinberg equilibrium study using Chi - square test showed that the studied population was not in Hardy - Weinberg equilibrium. Analy sis of phenotypic and genotypic data showed a significant association between genotypes of GH gene and live weights at 8 and 12 weeks of age and carcass weight. Significant associations were found between the GHR gene with live weight at 12 weeks of age an d carcass weight and also between IGF - 1 gene with abdominal fat and intramuscular fat ( P < 0.05 ). Generally, it can be concluded that GH, GHR and IGF - 1 genes can be used as candidate genes for improving growth and carcass traits in Mazandaran native fowls.

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