1. College of Animal Science and Veterinary Medicine, Shanxi Agricultural University, Taigu, Shanxi, China;
2. Jincheng Animal Husbandry and Veterinary Bureau, Jincheng, Shanxi, China;
3. Shanxi Animal Husbandry and Veterinary School, Taiyuan, Shanxi, China;
4. Department of Animal Science, Washington State University, Pullman, WA, USA