1. Department of Biomedical Sciences and Pathobiology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061
2. Department of Small Animal Clinical Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061
3. Laboratory of Veterinary Pathology, Department of Pharmacology and Pathobiology, Royal Veterinary and Agricultural University, Bulowsvej 17, DK-1870 Frederiksberg C, Denmark
4. Danish Institute of Agricultural Sciences, Department of Animal Breeding and Genetics, DK-8830 Tjele, Denmark