1. Department of Basic Sciences and Aquatic Medicine; The Norwegian School of Veterinary Science; Post-box 8146 Dep. N-0033 Oslo Norway
2. Department of Companion Animal Clinical Sciences; Section for Equine Medicine and Surgery; The Norwegian School of Veterinary Science; Post-box 8146 Dep N-0033 Oslo Norway
3. Department of Veterinary Population Medicine; University of Minnesota; St Paul MN 55108 USA
4. School of Statistics; University of Minnesota; Minneapolis MN 55455 USA
5. Department of Veterinary and Biomedical Sciences; University of Minnesota; St Paul MN 55108 USA