2.4 Samples collection
The eggs from the ducks of the experimental group and the control group were collected for hatching, and the fertilization rate and hatching rate of each group were counted. Collect eggs as early as possible every day to reduce the time that eggs are stored outdoors. Use a disinfectant to scrub the eggshells to prevent bacterial infections on the eggshells from affecting the hatching, and then place them in the incubator for hatching. On the 6th day of hatching, the yolk membrane was collected from the unfertilized eggs (Wei et al., 2020). The spleen of the dead embryos during the hatching process was collected, and the hatched ducklings also received spleen tissue for virus detection. Finally, samples that test positive are freeze-thawed for virus isolation.