1. Department of Animal Production, Kyushu National Agricultural Experiment Station, 2421 Suya, Nishigoshi, Kumamoto 861-11, Japan
2. Laboratory of Veterinary Physiology, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183, Japan
3. Laboratory Animal Science, Kitasato University, School of Veterinary Medicine and Animal Science, Aomori 034, Japan