1. Swine and Poultry Research Center, Shizuoka Prefectural Research Institute of Animal Industry, Kikugawa, Shizuoka, 439-0037, Japan
2. School of Agriculture, Tokai University, Minamiaso, Kumamoto, 869-1404, Japan
3. Shizuoka Prefectural Tobu Livestock Hygiene Service Center, Kannami, Shizuoka 419-0114, Japan