1. Department of Animal Science; University of California; Davis CA 95616 USA
2. College of Animal Science and Technology; Shandong Agricultural University; Taian Shandong 271018 China
3. Department of Poultry Science; Texas A&M University; College Station TX 77843 USA
4. College of Animal Science and Technology; China Agricultural University; Beijing 100193 China
5. Department of Animal Science; Iowa State University; Ames IA 50011 USA
6. Animal Breeding and Genomics Centre; Wageningen University; Wageningen the Netherlands