1. The Graduate School of Natural Science and Technology
2. Division of Animal science and Technology, Faculty of Agriculture, Okayama University, Okayama 700-8530, Japan
3. Harbin Veterinary Research Institute of CAAS, Harbin 150001, P.R. China
4. Department of Animal Science, University of Missouri-Columbia, Columbia, MO 65211, USA
5. Department of Animal Reproduction, National Institute of Animal Industry, Tsukuba, Ibaraki 305-0091, Japan