Random allocation of chickens into 5 groups including the PBS group, challenge group, empty vector group, profilin-FliC group, and profilin group, was conducted, with each group comprising 20 birds. The experimental timeline and group assignments are depicted in and, respectively.Oral immunization was administered to chickens aged 3,4, and 5 d, wherein 200 mL of recombinant live bacteria(1 £ 109 CFU per chicken) expressing NC8-pSIP409-pgsA0, NC8-pSIP409-pgsA0-profilin-FliC, or NC8-pSIP409-pgsA0-profilin, were administered.