1. Laboratory of Animal Breeding and Reproduction, Veterinary Medical Sciences, Graduate School of Agricultural and Life Sciences; The University of Tokyo; 1-1-1 Yayoi, Bunkyo-ku 113-8657 Tokyo Japan
2. Department of Gynecology and Obstetrics, Faculty of Medicine; Kyoto University; Sakyo-ku 606-8397 Kyoto Japan
3. Zen-noh ET center; 080-1407 Kamishihoro Hokkaido Japan
4. Department of Animal Sciences; University of Tennessee; 37996-4588 Knoxville TN USA