1. Key Laboratory for Animal Disease-Resistance Nutrition of China Ministry of Education, Institute of Animal Nutrition, Sichuan Agricultural University, Chengdu, P. R. China
2. Institute of Animal Genetics and Breeding, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu, P. R. China
3. State Key Lab of Animal Nutrition, College of Animal Science & Technology, China Agricultural University, Beijing, P. R. China