The effect of day old ocular vaccination with live intermediate infectious bursal disease virus (IBDV) vaccine was tested in commercial broiler chicks that have maternally derived antibodies (MDA) against infectious bursal disease virus (IBDV). Chicks were challenged with very virulent IBDV (vvIBDV) either at 24 days of age after being vaccinated at 1 and/or 14 days or at 31 days of age of those vaccinated at 1 or 14 and/or 21 days. The assessment of protection was determined by measuring, bursa / body weight (B: B) ratio, bursal index (BI), mean severity index (MSI) of bursal lymphoid tissue lesions and mortality rate at 7 days post-challenge (Pch), in addition, antibody response to IBDV at 14 days Pch.
Vaccination at 21, 14 & 21 and 1, 14 & 21 days of age protected 100% of vaccinated commercial broiler chickens only against mortality VvIBDV. However, none of the different vaccination regimes protected commercial broiler chickens neither from bursal atrophy nor bursal lesions. Serum IBDV antibody levels, as monitored by Enzyme-Linked Immunosorbent Assay (ELISA), showed similar rates of decline among non- vaccinated and all the vaccinated groups and by day 35 PV, serum antibody level in non vaccinated and vaccinated groups were below. detectable levels. Results of these studies indicate that IBDV vaccination at one day of age via eye drop doesn't protected against mortality, bursal atrophy and lesions and doesn't cause accelerated IBDV specific MDA. Moreover, the serological examination of optimal vaccination time for each flock is required to control of vvIBDV in the field.