The current study was supported by the National Natural Science Foundation of China (grant no. 31302195 ), the Natural Science Foundation of Hubei Province of China (grant no. 2011CDB225 ), and Hubei Collaborative Innovation Center for Animal Nutrition and Feed Safety, and International Science & Technology Cooperation Program of China (grant no. 2011DFG33280 ), and Major Science and Technology Program for Water Pollution Control and Treatment of Lake Chaohu (grant no. 2012ZX07103003-02-02 ). All authors also thank the anonymous reviewers for their helpful suggestions.