1. Key Laboratory of Agricultural Animal Genetics, Breeding & Reproduction of Ministry of Education; College of Animal Science & Technology; Huazhong Agricultural University; Wuhan 430070 China
2. The Key Laboratory for Domestic Animal Genetic Resources and Breeding of Ministry of Agriculture of China; Institute of Animal Science; Chinese Academy of Agricultural Sciences; Beijing 100193 China
3. Department of Animal Science and Center for Integrated Animal Genomics; Iowa State University; Ames IA 50011 USA