The kappa-casein gene has been extensively studied in cattle for its stabilizing role of the casein micelles and, therefore, its influence on the manufacturing properties of milk. In Holstein dairy cattle the B variant of kappa-casein (CSN3) is associated with a higher protein content, better quality of crud and increased yield of cheese. It has been suggested that identification of CSN3 genotypes could be an economically important selection criterion for dairy herds designated for industrial milk production (Pederson, J. 1991). Genotyping of milk proteins, such as CSN3, can be performed by electrophoresis, directly from milk samples, as the expression of the caseins occurs only during the lactation phase in mammary gland cells. Therefore, the use of electrophoresis for genotyping of milk proteins is strongly limited because it can only be used in cows in the lactation stage. With newly developed techniques based on DNA analysis, which include polymerase chain reaction and restriction fragment length polymorphisms (PCR-RFLP) methods, it is now possible to determine the CSN3 genotype of all individuals in a given population under selection, regardless of sex, age or physiological stage (Lara, M.A.C. et al. 2002). The Kappa-casein genotypes has not been detected so far in Sistani cows.