1. The United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan
2. Department of Clinically Veterinary Sciences, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan
3. Field Center of Animal Science, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan
4. Graduate School of Animal and Food Hygiene, Obihiro University of Agriculture and Veterinary Medicine, Hokkaido 080-8555, Japan