1. Veterinary Medical Center, Obihiro University of Agriculture and Veterinary Medicine, Nishi 3-sen 14, Inadacho, Obihiro, Hokkaido 080-8555, Japan
2. Laboratory of Small Animal Internal Medicine, School of Veterinary Medicine, Azabu University, 1-17-71 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5201, Japan
3. Department of Veterinary Medicine, Faculty of Veterinary Medicine, Rakuno Gakuen University, Bunkyodai Midorimachi 582, Ebetsu, Hokkaido 069-8501, Japan