1. Institute of Livestock and Grassland Science, National Agriculture and Food Research Organization, 2 Ikenodai, Tsukuba, Ibaraki 305-0901, Japan.
2. Global Pig Farms, Inc., 800, Kamihakoda, Hokkitsu-machi, Shibukawa-shi, Gunma, 377-0052, Japan.
3. Graduate School of Agricultural Science, Tohoku University, 468-1 Aramaki Aza Aoba, Aoba-ku, Sendai, Miyagi, 980-8572, Japan.