1. From the Departments of Veterinary Clinical Sciences (DiBartola) and Veterinary Pathobiology (Tarr), College of Veterinary Medicine, The Ohio State University, 1935 Coffey Rd, Columbus, OH 43210, the Animal Disease Diagnostic Laboratory, School of Veterinary Medicine, Purdue University, West Lafayette, IN 47907 (Webb), and Section of Medical Genetics, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104 (Giger).