1. Reproductive Biology and Technology Research Team, National Institute of Livestock and Grassland Science, Tsukuba, Ibaraki 305-0901, Japan.
2. National Livestock Breeding Center, Nishigo-mura, Fukushima 961-8511, Japan.
3. Ibaraki Livestock Research Center, Ishioka, Ibaraki 315-0132, Japan.
4. Kochi Prefectual Livestock Experiment Station, Takaoka-gun, Kochi 789-1233, Japan.
5. National Institute of Animal Health, Tsukuba, Ibaraki 305-0856, Japan.