1. Department of Clinical Veterinary Medicine, Obihiro University of Agriculture and Veterinary Medicine, Inada, Obihiro, Hokkaido 080–8555, Japan
2. Animal Research Center, Hokkaido Research Organization, Sintoku, Hokkaido 081–0038, Japan
3. Industrial Research Institute, Hokkaido Research Organization, Kita 19, Nishi, 11, Kita-ku, Sapporo, Hokkaido 060–0819, Japan
4. School of Veterinary Medicine, Rakuno Gakuen University, 582 Midorimati, Bunkyodai, Ebetsu, Hokkaido 069–8501, Japan