1. Equine Research Institute, Japan Racing Association, Tochigi 320-0856, Japan
2. Epizootic Research Center, Equine Research Institute, Japan Racing Association, Tochigi 329-0412, Japan
3. Research Institute for Animal Science in Biochemistry and Toxicology, Kanagawa 229-1132, Japan
4. Livestock Farming Promotion Division, Bureau of Food Safety Promotion, Department of Agriculture, Hokkaido Government, Hokkaido 060-0003, Japan