School of Agriculture, Liaocheng University, Liaocheng 252059, P.R.China;
School of Veterinary Medicine, Shandong Agricultural University, Tai’an 271018, P.R.China;
China Animal Health and Epidemiology Center, Qingdao 266032, P.R.China;
School of Veterinary Medicine, Shandong Agricultural University, Tai’an 271018, P.R.China;