Stephen W. Barthold, DVM, MS, PhD, Dipl. ACVP, Hon. Member ACLAM, is Distinguished Professor Emeritus of Veterinary and Medical Pathology at the University of California, Davis, and former Director of the UC Davis Center for Comparative Medicine. He has over 40 years of experience in laboratory animal pathology. Stephen M. Griffey, DVM, PhD, is Clinical Professor of Laboratory Animal Pathology and Director of the Comparative Pathology Laboratory at the UC Davis School of Veterinary Medicine. He has over 20 years of experience in laboratory animal pathology. Dean H. Percy, DVM, MSc, PhD, Dipl. ACVP, is Professor Emeritus and former Chair of the Pathobiology Department, Ontario Veterinary College, Guelph, Ontario. He has over 50 years of experience in veterinary pathology and laboratory animal pathology.