1. National Center for International Research on Animal Genetics, Breeding and Reproduction / Key Laboratory of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, College of Animal Science and Technology Huazhong Agricultural University Wuhan 430070 P. R. China
2. Key Laboratory of Animal Genetics and Breeding of the Ministry of Agriculture, College of Animal Science and Technology China Agricultural University Beijing 100193 P. R. China
3. National Engineering and Technology Research Center for Livestock Wuhan 832003 P. R. China
4. Hubei Provincial Center of Technolgy Innovation for Domestic Animal Breeding Wuhan 100193 P. R. China
5. College of Animal Science and Technology Shihezi University Shihezi 832003 P. R. China