Model of the BNP-etiology. Dams vaccinated with PregSure® BVD which carry the MHC I variant(s) of the vaccine on their cells (top left dam, MHC I colored in red) do not produce MHC I alloantibodies and their offspring does not develop BNP. If the MHC I variant(s) on the cells differ from MHC I variant(s) from the vaccine (top right dam, MHC I colored in blue) alloantibody production is induced. In this case the development of BNP depends on hereditary transmission of paternal MHC I variants. If the paternal MHC I variants are not recognized by the alloantibodies no BNP will occur (bottom left calf). BNP syndrome only appears if the paternal MHC I variants match with the MHC I variants present in the PregSure® BVD vaccine (bottom right calf). Calves of both genders develop BNP equally as gene loci for MHC I are located on an autosome (chromosome 23).