1. Animal Resource Science Center, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Ibaraki 319-0206, Japan
2. Laboratory of Animal Breeding, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan
3. Laboratory of Veterinary Physiology, Department of Veterinary Medicine, Tokyo University of Agriculture and Technology, Tokyo 183-8509, Japan
4. Hidaka Training Research Center, Japan Racing Association, Hokkaido 057-0171, Japan
5. Laboratory of Theriogenology, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan