1. Department of Veterinary Medicine, College of Veterinary Medicine, National Chung Hsing University, Taichung 402, Taiwan
2. Graduate Institute of Veterinary Public Health, National Chung Hsing University, Taichung 402, Taiwan
3. Department of Safety Health and Environmental Engineering, Central Taiwan University of Science and Technology, Taichung 406, Taiwan
4. Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA, USA