The authors wish to thank Qiang Yu, Jiwei, Peng, Dian, Yang for their assistance in the experiment. This study was supported by the National Natural Science Foundation of China (grant no. 31672666 , 31302195 ), the Natural Science Foundation of Hubei Province of China (grant no. 2016CFB389 ), Educational Commission of Hubei Province (grant no. D20151705 ), and Hubei Collaborative Innovation Center for Animal Nutrition and Feed Safety . We would like to thank Pei Zhang and An-na Du from the Core Facility and Technical Support, Wuhan Institute of Virology, for their help with producing TEM micrographs. Thanks are also given to the anonymous reviewers for their helpful suggestions.
