1. From the Departments of Small Animal Medicine and Surgery (Fossum, Forrester, Miller, Boothe) and Large Animal Medicine (Cohen), College of Veterinary Medicine Texas A&M University, College Station, TX 77843, and the Departments of Veterinary Pathobiology (Swenson) and Veterinary Clinical Sciences (Birchard), College of Veterinary Medicine The Ohio State University, Columbus, OH 43210.