1. Laboratory of Theriogenology, Department of Clinical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Hokkaido 060-0818, Japan
2. Noboribetsu Bear Park, Hokkaido 059-0515, Japan
3. Laboratory of Theriogenology, Department of Clinical Sciences, Division of Veterinary Medicine, Faculty of Veterinary Medicine, Hokkaido University, Hokkaido 060-0818, Japan