1. Division of Animal Breeding and Reproduction Research, Institute of Livestock and Grassland Science, National Agriculture and Food Research Organization (NARO), Ibaraki 305-0901, Japan
2. Division of Livestock and Forage Research, Tohoku Agricultural Research Center, NARO, Morioka 020-0198, Japan
3. Laboratory of Veterinary Physiology, Iwate University, Iwate 020-8550, Japan