1. College of Veterinary Medicine, Northeast Agricultural University, Harbin 150030, P.R. China
2. College of Veterinary Medicine, Qingdao Agricultural University, Qingdao 266109, China
3. Key Laboratory of the Provincial Education Department of Heilongjiang for Common Animal Disease Prevention and Treatment, Northeast Agricultural University, Harbin 150030, P.R. China
4. Heilongjiang Key Laboratory for Laboratory Animals and Comparative Medicine, Northeast Agricultural University, Harbin 150030, P.R. China