Methods for testing bovine for resistance or susceptibility to persistent lymphocytosis by detecting polymorphism in BoLA-DR3 exon 2

The present disclosure provides a method for evaluating resistance of an animal of the genus Bos to persistent lymphocytosis. The method includes the steps of (a) obtaining a sample of DNA from the animal that includes a DRB3 gene exon 2; (b) identifying nucleotides of the DRB3 gene exon 2; and (c) determining whether the nucleotides contain codons that encode a glutamic acid at position 70 and an arginine at position 71, a valine at position 75, an aspartic acid at position 76, a threonine at position 77, and a tyrosine at position 78 of the DRB3 gene product, the presence of which codons indicates susceptibility to persistent lymphocytosis. Kits containing primers that hybridize to nucleotide positions 70 and 71 or 75-78 of the DRB3 gene exon 2 are also provided.