Background and Objective: Growth and differentiation factor-8, is a protein secreted from in muscle and adipose tissues, also referred to as Myostatin -MSTN-. MSTN is considered to be one of the most powerful negative regulators of muscle growth The control of MSTN gene expression by genetic engineering can accelerate muscle growth and animal production without side effects. The MSTN gene is located on bovine chromosome 2 and consists of three exons and two introns. An insertion/deletion mutation in the MSTN gene has a significant effect on the increase of the body weight and improvement of carcass traits such as lean meat percentage, known as double-muscled cattle. This characteristic has been caused by a fixed mutation in MSTN gene in this breed. Recently there are increasing interests to cross this breed with other dairy breeds to produce hybrids of beef and dairy cattle. Therefore, there is a demand to detect the genotype of calves at birth. This study has been carried out with the objective of mutation Materials and Methods: Genomic DNA was extracted from 18 biological samples including 1 Belgian Blue-Jersey and 9 blood samples from Belgian Blue-Holstein hybrid individuals, seven blood samples from pure Holstein cows and also 1 semen sample from pure Belgian Blue breed. A pair of specific primers designed to amplify a fragment of 176 bp from exon III of myostatin gene. PCR reactions in a volume of 15 μl were performed followed by a HRM program including melting curve and difference graph analysis. Findings: DNA extraction and PCR amplification was done successfully. Results showed that as expected, 3 distinctive melting peaks were observed belonging to pure Belgian Blue -with two alleles of mutated MSTN-, Belgian Blue hybrids -Only one mutated allele for MSTN- and Holstein -wild type alleles for MSTN- individuals. Melting peaks had a range between 80 and 82 °C. Belgian Blue hybrid individuals showed a double peak in melting temperature. Conclusion: By using this method, genotyping of MSTN gene in cattle can be done quickly with a high precision.

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