1. Key laboratory of Animal Genetics, Breeding and Reproduction of Shaanxi Province; College of Animal Science and Technology; Northwest A&F University; Yangling Shaanxi 712100 China
2. Yunnan Academy of Grassland and Animal Science; Kunming Yunnan 650212 China
3. Branch of Animal Science; Jilin Academy of Agricultural Sciences; Gongzhuling Jilin 136100 China
4. Academy of Animal Science and Veterinary Medicine; Qinghai University; Xining Qinghai 810016 China