1. Hokkaido University Veterinary Teaching Hospital, Kita-19jo Nishi-10, Kita-ku, Sapporo, Hokkaido 060-0819, Japan
2. North Lab., 8-35 Hondori 2 Kita, Shiroishi-ku, Sapporo, Hokkaido 003-0027, Japan
3. Department of Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Kita-18jo Nishi-9, Kita-ku, Sapporo, Hokkaido 060-0818, Japan