1. Institut für Tierzucht, Bundesforschungsanstalt für Landwirtschaft; D-31535 Neustadt-Mariensee Germany
2. Office of Research, Center for Veterinary Medicine, U.S. Food and Drug Administration; Laurel MD 20708
3. Animal Disease Diagnostic Laboratory, Department of Veterinary Pathobiology; Purdue University School of Veterinary Medicine; West Lafayette IN 47907-2065