1. Key Laboratory of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, Huazhong Agricultural University, Wuhan, P. R. China
2. Mianyang Academy of Agricultural Sciences, Mianyang, P. R. China
3. Laboratory of Sheep and Goat Genetics, Breeding and Reproduction, College of Animal Science and Technology, Huazhong Agricultural University, Wuhan, P. R. China