ABSTRACT Milk protein polymorphisms have received considerable interest because of their potential use as an aid to genetic selection and genetic characterization of bovine breeds. In Holstein dairy cattle the B variant of Kappa-Casein (CSN3) is associated with a higher protein content, better quality of crude and increased yield of cheese. It had been suggested that identification of CSN3 genotypes could be an economically important selection critrion for dairy herds designed for industrial milk production. Identification of A and B alleles of K-Casein was performed by amplification of a 228 bp DNA fragment, located in exon IV, by means of PCR-RFLP method. Peripheral blood was sampled from 25 (Kenehbist farm) and 64 (Nemoneh farm) Holstein cattles. DNA was extracted and a 228 bp fragment of genomic DNA was amplified in PCR reactions by standard methods. The amplicon then was digested with HinfI or HindIII restriction endonucleases. Genotypic frequencies were 12.00% and 21.87% for AA, 88.00% and 56.25% for AB and 00.00% and 21.87% for BB in Kenehbist and Nemoneh farm rspectively. Frequencies of alleles A and B were 0.56 and 0.44 in Kenehbist farm and 0.50 and 0.50 in Nemoneh farm. The Nei\'s heterozygosity value of K-CN locus for Kenehbist farm was 49.28% and for Nemoneh farm was 50.00%. The Kenehbist farm was not in Harrdy-Weinberg equilibrium. Differences in the profile of allele and genotype frequencies of K-CN locus between farms studied were revealed. KEYWORDS Kappa-casein, genotyping, PCR, RFLP.

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