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 Association, Sapporo 060–0004, Japan