1. Graduate School of Animal and Food Hygiene, Obihiro University of Agriculture and Veterinary Medicine, 080-8555 Obihiro, Japan
2. Field Center of Animal Science and Agriculture, Obihiro University of Agriculture and Veterinary Medicine, 080-8555 Obihiro, Japan
3. Laboratory of Reproductive Endocrinology, Graduate School of Natural Science and Technology, Okayama University, 700-8530 Okayama, Japan
4. Division of Bioimaging Sciences, Center for Molecular Medicine, Jichi Medical University, 329-0498 Tochigi, Japan