1. Department of Genetic Resources II, National Institute of Agrobiological Resources, Tsukuba, Ibaraki 305-8602, Japan
2. School of Veterinary Medicine, Azabu University, Sagamihara, Kanagawa 229-8501, Japan
3. Department of Animal Production, Tohoku National Agricultural Experiment Station, Morioka, Iwate 020-0123, Japan
4. YS New Technology Institute, Inc., Ishibashi, Shimotsuga, Tochigi 329-0512, Japan