1. United Graduate School of Veterinary Science, Gifu University, Gifu 501-1193, Japan
2. Miyagi Prefectural Federated Agricultural Mutual Aid Association, Miyagi 980-0011, Japan
3. Faculty of Science, Kyushu University, Fukuoka 819-0395, Japan
4. Graduate School of Agricultural Science, Tohoku University, Miyagi 980-0845 Japan
5. Araseki Farm, Miyagi 987-0281, Japan
6. Cooperative department of Veterinary Medicine, Faculty of Agriculture, Iwate University, Iwate 020-8550, Japan