Evaluation of the immune response of layer chickens to Newcastle disease virus vaccines using the new vaccination regimens.

Background: The study aimed to evaluate the immunological response of layer chickens to live Newcastle disease virus vaccine using a newly developed vaccine schedule administered via the ocular route, as well as assess the persistence of passive antibodies in layer chickens and the effectiveness of protection against strains of the virus.

Methods: A total of 140-day-old Lohmann Brown chicks were randomly divided into seven groups, 20 chicks each. Groups 1-3 received a single eye instillation of the vaccine at ages 5, 26 and 54 days, respectively, whereas groups 4-6 received a double eye instillation. Group 7 served as non-vaccinated control group. Ten days after immunization, samples were taken from hens that had received the vaccine at ages 15, 36 and 64, as well as from control chickens that had not received the vaccine at ages 5, 15, 21 and 31.

Results: A total of 10 serum samples from all chickens exhibited protective antibodies, and booster doses resulted in the highest haemagglutination inhibition titre. No significant change in antibody production was observed among layer hens (p > 0.05). The study found that the La Sota (GMT ± SD: 6.71 ± 4.96), La Sota (GMT ± SD: 8.00 ± 0.00) and thermostable I2 (GMT ± SD: 7.60 ± 6.02), vaccination schedules provided the maximum immune response in single eye instillation, whereas the HB1 (GMT ± SD: 7.11 ± 4.77), La Sota (GMT ± SD: 7.83 ± 5.76) and La Sota (GMT ± SD: 7.60 ± 6.02), combination was the second-best vaccination schedule in double eye instillation. Furthermore, maternally-derived antibodies were maintained up to 31 days of age, indicating the level of passive immunity prior to vaccination. Characteristic lesions, such as edematous and diphtheria mucosal membranes of the trachea, along with petechial and necrotic haemorrhages of the proventriculus, were observed during the necropsy of the birds that died from the challenged virus.

Conclusion: This study suggests that subsequent live virus vaccine by ocular route immunization is required to effectively protect against velogenic viscerotropic Newcastle disease infection. The results also highlight the importance of developing effective vaccination schedules and routes to enhance immunity against ND in layer chickens.