1. Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, 2407 River Drive, Knoxville, Tennessee 37996, USA
2. Current address: College of Veterinary Medicine, University of Georgia, Athens, Georgia 30602, USA
3. Current address: Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois, 3516 Veterinary Medicine Basic Sciences Building, 2001 South Lincoln Avenue, Urbana, Illinois 61802, USA
4. Department of Comparative Medicine, College of Veterinary Medicine, University of Tennessee, 2407 River Drive, Knoxville, Tennessee 37996, USA