1. Racehorse Hospital, Ritto Training Center, Japan Racing Association, 1028, Misono, Ritto, Shiga 520–3085, Japan
2. Obihiro University of Agriculture and Veterinary Medicine, 2–11, Inada-cho, Obihiro, Hokkaido 080–8555, Japan
3. Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California Davis, One Garrod Drive, Davis, California 95616, U.S.A.