CLASSIFICATION OF ALLELES OF A MULTIALLELIC LOCUS IN THE STUDY OF GENETIC ASSOCIATION WITH THE DEVELOPMENT OF DISEASES

JULIARENA MARCELA; RODRIGUEZ EDGARDO; CERIANI MARIA CAROLINA; GUTIERREZ SILVINA; ESTEBAN EDUARDO

Florianopolis

Congreso; XXVth International Biometric Conference; 2010

International Biometric Society

The bovine MHC genes (BoLA) are particularly interesting because they are associated with genetic resistance and susceptibility to a wide array of diseases. Moreover, BoLA appears to influence other productive and reproductive traits. The essential feature of these genes is that they maintain, at the population level, a large diversity or polymorphism and that they present codominance or simultaneous expression of two alleles present in the animal. A total of 230 Holstein, bovine leukaemia virus (BLV)-infected cattle belonging to seven dairy herds located in different regions of Argentina were selected for this study. Previously, cattle were classified into two infection profiles characterized by low and high proviral loads (LPL and HPL, respectively). Here, the influence of the polymorphism at the BoLA-DRB3.2* gene of these animals was examined. In the population studied, we identified 29 alleles defined according to the ISAG BoLA Nomenclature Committee. We calculated the allelic frequencies and then compared the distribution frequency of alleles in the LPL and HPL profiles using a general chi-squared test in order to examine the contribution of each allele to the total chi-squared value. Considering that low allelic frequencies increase the probability of spurious significant associations of alleles with the infection profile, results obtained with alleles having a frequency below 2% are clustered in a group. The association between the BoLA-DRB3.2* alleles and the LPL and HPL profiles was determined as the odds ratio (OR). According to the ORs obtained, the DRB3 alleles were assigned to three categories: susceptible (S) (OR <1, p < 0.05), resistant (R) (OR > 1, p < 0.05) and neutral (N) (p > 0.05, irrespective of OR number). Based on their DRB3 genotype, cattle were classified into six possible genotypes (NN, NR, NS, RR, RS or SS). The environmental effect (herd) and the effect of the genotypes was evaluated for infection profiles (LPL and HPL) using a logistic regression model. This analysis indicated that genotype category significantly influenced this variable (p < 0.0001), while herd effect did not (p = 0.2541). The definition of genotypes according to the classification of alleles into classes (R, S and N) allowed us to demonstrate that there is a strong association between the RR and RN genotypes with the LPL profile, while the SS and NS genotypes were associated with the HPL profile. The RS genotype could not be associated with any particular profile. Our results show that some alleles appear to be the best BLV resistance markers in Holstein cattle.