1. Institute of Animal Husbandry and Veterinary Medicine, Tibet Academy of Agriculture and Animal Husbandry Sciences, Lhasa 850009, China
2. Linzhou Animal Husbandry and Veterinary Station, Lhasa 850009, China
3. College of Veterinary Medicine, Gansu Agricultural University, Lanzhou 730070, China
4. College of Veterinary Medicine, Nanjing Agricultural University, Nanjing 210095, China