1. Department of Veterinary Medicine, Obihiro University of Agriculture and Veterinary Medicine, Inada, Obihiro, Hokkaido 080-8555, Japan
2. Industrial Research Center, Hokkaido Research Organization, Kita 19, Nishi 11, Kita-ku, Sapporo, Hokkaido 060-0819, Japan
3. Animal Research Center, Hokkaido Research Organization, Sintoku, Hokkaido 081-0038, Japan
4. Dairy Research Center, Hokkaido Research Organization, Asahigaoka, Nakashibetsu, Hokkaido 086-1135, Japan
5. School of Veterinary Medicine, Rakuno Gakuen University, 582 Midorimati, Bunkyodai, Ebetsu, Hokkaido 069-8501, Japan