1. Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima 739-8528, Japan, Department of Animal Products, National Institute of Livestock and Grassland Science, Tsukuba, Ibaraki 305-0901, Japan, and Research and Development Center, Nippon Meat Packers, Inc., 3-3 Midorigahara, Tsukuba, Ibaraki 300-2646, Japan