1. Department of Animal, Dairy, and Veterinary Sciences, Utah State University, Logan, Utah.
2. Institute of Animal Genetics and Breeding, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu, P.R. China.
3. College of Animal Science, South China Agricultural University, Guangzhou, P.R. China.
4. College of Animal Science and Technology, Gansu Agricultural University, Lanzhou, P.R. China.