ACKNOWLEDGEMENTS
We are very grateful to Mr. Changyu Ma (Henan Xurui duck industry Co. Ltd) for kindly providing the healthy duck embryos and the epidemic information. This work was supported by the grants from Key Scientific Research Foundation of the Higher Education Institutions of Henan Province (19B230010), Scientific Innovation Fund of Henan University of Animal Husbandry and Economy (XKYCXJJ2020011), Youth Science Foundations of Henan University of Animal Husbandry and Economy (2021HNUAHEDF004) and Scientific Innovation Team Project of Henan University of Animal Husbandry and Economy (2018KYTD13).