1. College of Animal Science and Technology, Southwest University, Beibei, Chongqing, P. R. China
2. Chongqing Key Laboratory of Forage and Herbivore, Beibei, Chongqing, P. R. China
3. Chongqing Engineering Research Center for Herbivores Resource Protection and Utilization, Beibei, Chongqing, P. R. China