Fig. 5.

Analysis of protection against lethal vvIBDV-HLJ0504 challenge determined by calculating BBIX values and detecting specific neutralizing antibodies. a BBIX values of chickens after vvIBDV challenge. Dead birds were dissected on the day they died, and surviving birds were euthanized and analyzed after the observation period on day 10 post challenge. The data presented are the mean ± standard deviation (SD) from 15 birds in both the injected and oral r-L. lactis-OptiVP2-RCK groups, 11 birds in the healthy control group, and 10 birds in the oral r-L. lactis-OptiVP2 group. b Detection and comparison of virus neutralization antibodies against IBDV in chickens 14 days after vaccination. Statistical significance was set at *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001