1. College of Veterinary Medicine, Shanxi Agricultural University, Taigu 030801, Shanxi, P.R. China
2. Shanxi Key Laboratory of Environmental Veterinary Medicine, Shanxi Agricultural University, Taigu 030801, Shanxi, P.R. China
3. College of Life Sciences, Shanxi Agricultural University, Taigu 030801, Shanxi, P.R. China
4. Department of Basic Science, Shanxi Agricultural University, Taigu 030801, Shanxi, P.R. China