1. Animal Disease-Resistance Nutrition, Ministry of Education, Ministry of Agriculture and Rural Affairs, Key Laboratory of Sichuan Province, Animal Nutrition Institute, Sichuan Agricultural University , Chengdu 611130, Sichuan , P. R. China
2. College of Science, Sichuan Agricultural University , Xin Kang Road, Yucheng District, Ya’an 625014 , P.R. China