Fig. 4

Animal experiment program and protective efficacy of recombinant r-L. lactis-OptiVP2-RCK against vvIBDV challenge. a Schematic diagrams of animal immunization, antibody detection and virus challenge. Briefly, SPF chickens were vaccinated at 15 days old. At 35 days old, chickens were challenged with 1000 ELD50 of vvIBDV viruses via intranasal and intraocular routes. And at 10 days post challenge (45 days old), surviving animals were sacrificed and necropsy was performed including pathological examination and bursal index. Throughout the animal experiment, serums were collected at 15, 23, 30, 35 and 45 days old for detect the ELISA antibody and neutralization antibody. b Protective efficacy of r-L. lactis-OptiVP2-RCK against vvIBDV (0504) challenge. Survival rates of chickens challenged with vvIBDV over an observation period of 10 days