The Bovine Leukemia Virus (BLV) is a retrovirus that affects the immune system of cattle as their target cells are B lymphocytes. Some polymorphisms at the BoLA-DRB 3.2 gene have been associated with resistance/susceptibility to diseases. The objective of this research was to determine the polymorphisms at the BoLA-DRB 3.2 gene and associate them with resistance (R), neutrality (N) or susceptibility (S) to BLV in a Holstein cow population.500 blood samples were taken. Nested PCR was performed for detecting BLV virus and PCR-RFLP was performed to identify alleles of gene BoLA-DRB 3.2. Susceptibility was determined using odds ratio (OR) and P value. According to their genotype, cows were classified in homozygous (R/R, N/N, or S/S) and heterozygous (R/N, R/S, N/S). BLV molecular prevalence was 44%. The most frequent allele was BoLA-DRB3.2*22 (16.8%), alleles associated with resistance to BLV were BoLA-DRB3.2*8 (OR=1.489; P<0.10) and BoLA-DRB3.2*12 (OR=3.897; P<0.10) and allele BoLA-DRB3.2*16 (OR=0.710; P<0.10) was associated with susceptibility. Allele BoLA-DRB3.2*8 had the highest allelic frequency for negative cows (0.19). 63.7% of cows with genotype RN and 70% of cows with genotype RR were resistant to infection by BLV. Alleles R and S have a dominant effect on allele N (P<0.05). The use of reliable diagnostic techniques in conjunction with identification of resistant or susceptible animals can monitor the progress of the disease in dairy herds. Alleles BoLA-DRB3.2*8 and *12 were positively related to the disease and therefore cows have low risk of infection, unlike allele BoLA-DRB3.2*16 which was negatively related and animals have high risk for the disease.

Key words: BoLA-DRB3.2, Bovine leukemia virus, Nested PCR, Prevalence, Resistance