1. Division of Bioscience, Graduate School of Science and Technology, Kobe University, Kobe 657-8501, Japan
2. Department of Animal Reproduction, National Institute of Animal Industry, Tsukuba 305-0901, Japan
3. Department of Biosciences and Technology, Faculty of Agriculture, Iwate University, Morioka 020-8550, Japan
4. Department of Animal Science, Faculty of Agriculture, Kobe University, Kobe 657-8501, Japan