1. Division of Livestock and Grassland Research, Kyushu Okinawa Agricultural Research Center, NARO, Kumamoto 861-1192, Japan
2. Department of Reproductive Immunology and Pathology, Institute of Animal Reproduction and Food Research, Polish Academy of Sciences, Olsztyn, Poland
3. Obihiro University of Agriculture and Veterinary Medicine, Obihiro 080-8555, Japan