1. Department of Animal Science and Technology, Chung-Ang University, Ansung, Gyeonggi-do 456-756, Korea
2. BET Research Institute, Chung-Ang University, Ansung, Gyeonggi-do 456-756, Korea
3. Department of Life Science, College of Natural Sciences, Hanyang University, Seoul 133-791, Korea
4. Department of Science, Spokane Community College, 1810 N Greene Street, Spokane, WA 99217-5399