1 National Engineering Laboratory for Animal Breeding and Key Laboratory of Animal Genetics, Breeding and Reproduction, MARA; College of Animal Science and Technology, China Agricultural University, No. 2 Yuanmingyuan West Rd, Beijing, 100193, China.
2 National Engineering Laboratory for Animal Breeding and Key Laboratory of Animal Genetics, Breeding and Reproduction, MARA; College of Animal Science and Technology, China Agricultural University, No. 2 Yuanmingyuan West Rd, Beijing, 100193, China. zchou@cau.edu.cn.