1. State Key Laboratory of Veterinary Etiological Biology, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu Province 730046, PR China
2. College of Animal Science and Technology, Jiangxi Agricultural University, Nanchang, Jiangxi Province 330045, PR China
3. College of Animal Science and Technology, Jilin Agricultural University, Changchun, Jilin Province 130118, PR China