1. Laboratory of Animal Breeding and Reproduction, Division of Animal Science, Faculty of Agriculture, Utsunomiya University, 350 Mine-Machi, Utsunomiya, Tochigi 321-8505, Japan
2. Center for Bioscience Research and Education, Utsunomiya University, 350 Mine-Machi, Utsunomiya, Tochigi 321-8505, Japan