1. Laboratory of Theriogenology, Department of Veterinary Clinical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
2. Dairy Cattle Group, Konsen Agricultural Experiment Station, Hokkaido Research Organization, Nakashibetsu 086-1135, Japan
3. Genetics Hokkaido, Sapporo 060-0004, Japan