Allelic polymorphism in exon 2 of the BoLA-DRB3 gene in Iranian Holstein cattle

Major histocompatibility complex (MHC) of vertebrates comprises a group of genes, which plays a central role in immune response and includes MHC- class I, II and III. The bovine MHC system is known as BoLA and its corresponding genes are located on chromosome 23. The BoLA-DRB3.2 genes are part of the MHC class II in cattle. These genes are highly polymorphic, found to be associated with resistance/susceptibility to infections and also with fertility, growth and milk production parameters. Polymorphism of exon 2 of the BoLA-DRB3 gene was detected by the PCR-RFLP method in 350 Iranian Holstein cattle. After DNA extraction, second exon of BOLA-DRB3 was amplified by the seminested PCR method. The fragments produced by amplifying second exon were cut by three enzymes, RsaI, PsuI and HaeIII. In restriction fragment analysis 18, 5 and 6 different allelic patterns were observed for RsaI, PsuI and HaeIII restriction enzymes, respectively. In total, 48 different alleles were detected where 9 out of 48 alleles were previously unreported. Allelic frequencies, genotype frequencies, expected and observed homozygosty and heterozygosity were calculated. The other step was evaluating the frequencies of alleles mediating resistance and susceptibility to Bovine leukosis(BLV), Foot and mouth disease (FMD), mastitis and somatic cell count (SCC), Cystic ovarian disease, some parasitic infections and increasing or decreasing milk production traits. The result of this study indicates that the exon 2 region of BoLA-DRB3 gene is highly polymorphic in the Iranian Holstein cattle. Also the high presence of alleles that are sensitive to BLV, mastitis, FMD and to some extent tick borne disease was a remarkable point. Alleles associated with susceptibility to BLV were most frequent. Frequency of alleles associated with milk production traits was similar to previous studied populations