Through TUNEL assay, flow cytometry, and apoptotic pathway analysis, Our analysis revealed that H5N6 AIV infection markedly upregulates apoptotic genes such as Fas, FADD, caspase-8, BAK, cytochrome c, APAF1, caspase-9, and caspase-3 (P < 0.05), thereby promoting apoptosis in DEFs. This evidence concerns the gene CASP9 and infection.