Key Laboratony for Anima/Genetics;
Breeding and Reproduction of Shaanxi Province;
College of Animal Science and Technology;
Northwest A&F University;
Yangling;
Shaanxi 712100;
China;
Key Laboratory for Animal Disease Resistance Nutrition of the Ministry of Education of China;
Institute of Animal Nutntion;
Sichuan Agricultural University;
Chengdu;
Sichuan 611100;
China;