1. Animal Breeding and Reproduction Research Division, NARO Institute of Livestock and Grassland Science, 2 Ikenodai, Tsukuba, Ibaraki 305–0901, Japan
2. Ehime Research Institute of Agriculture, Forestry an Fisheries, 7–156 Ashimo, Nomura, Iyo, Ehime 797–1211, Japan
3. Livestock Technology Promotion Center, 695 Yamamoto, Hino, Gamou, Shiga 529–1651, Japan
4. Livestock and Grassland Research Division, NARO Kyushu Okinawa Agricultural Research Center, Suya 2421, Koshi, Kumamoto 861–1192, Japan
5. Laboratory of Reproductive Endocrinology, Graduate School of Natural Science and Technology, Okayama University, 3–1–1, Tsushimanaka, Okayama, Okayama 700–8530, Japan
6. National Institute of Animal Health, Kannondai, Tsukuba, Ibaraki 305–0856, Japan