1. Department of Animal Breeding and Genetics, College of animal science, Shanxi Agricultural University, Taigu, Shanxi, P.R. China
2. Department of Animal Breeding and Genetics, College of Animal Science and Technology, Shandong Agricultural University, Taian, Shandong, P.R. China
3. Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa, Honolulu, HI, USA