Two groups of mastitis-susceptible (n = 43) and resistant (n= 42) cows were selected and examined for particular alleles. In this study, cows with a history of mastitis treatment of more than 5 times during 1 to 3 parities were classified as susceptible, and cows with no mastitis treatment until the end of parity 3 were classified as resistant. Clinical mastitis was diagnosed by the farm veterinarian.