1. Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
2. Current affiliation: Maebashi Institute of Animal Science, Livestock Improvement Association of Japan, Inc., Maebashi, Gunma 371-0121, Japan
3. Shirakawa Institute of Animal Genetics, Japan Livestock Technology Association, Yushima, Bunkyo-ku, Tokyo 113-0034, Japan
4. Current affiliation: Satoyama Division, Sado Island Center for Ecological Sustainability, Niigata University, Niigata 952-0103, Japan