Lack of evidence for an association between MHC diversity and the development of bovine neonatal pancytopenia in Holstein dairy cattle.

Bovine neonatal pancytopenia (BNP), a disease of neonatal calves, has been described in a number of European countries since 2006. The disease results in high mortality of calves aged 1-4 weeks and is characterised by severe bone marrow pathology resulting in profound thrombocytopenia and consequent haemorrhagic diathesis. A number of hypotheses including a novel virus infection, plant toxins, a vaccine associated isoimmune disease, or a genetic defect have been suggested to explain the aetiology of this disease. However, as the number of cases in affected herds remains small, it is hypothesised that the genetic background of the calf may influence disease susceptibility. To test this we focused on the class II region of the major histocompatibility complex (MHC) which is often associated with variations in immune response and susceptibility to antibody mediated autoimmune disease. Forty-three cases of BNP and sixty-eight controls were genotyped at the polymorphic class II MHC-DRB3 locus. Twenty DRB3 alleles were identified with seven appearing at frequencies ≥ 0.05. A comparison of the allelic frequencies between diseased and control groups showed that there was no evidence for any significant differences, suggesting that the MHC does not appear to be a predisposing risk factor in the development of BNP in Holstein dairy cattle.