One hundred and sixty one-day-old chicks were vaccinated in this study. They were divided into 4 groups; group I and II were vaccinated with single live attenuated vaccine either Newcastle disease vaccine or Infectious Bronchitis vaccine separately, while group III was vaccinated with a combined ND and IB vaccine. All birds were vaccinated via occulonasal route. The fourth group was kept as non vaccinated negative control. Two weeks post vaccination the 4 groups were subdivided into two subgroups A and B, twenty birds per each. Subgroup A was boostered with single ND vaccine in all 3 groups while subgroup B was boostered with single IB vaccine in all the three groups. Two weeks post second vaccination, all birds were challenged with virulent NDV. The level of antibodies and the protection percentage were determined using different serological methods. The results showed that: 1- The Arithmetic Mean (AM) HI titer in the first
group (Group I was 2.5 Log2 2 weeks after boostering with either ND or IB in birds of
subgroup A and subgroup B respectively. The 2- In the second group (group II), the arithmetic
mean (AM) HI titer was 3 Log2 2 weeks post vaccination with IB vaccine. After boostering with either ND or IB, the (AM) HI titer was 5 Loge 2 weeks post vaccination in birds of subgroup A and
subgroup B respectively. 3- The third group (group III), the (AM) HI titer was
2.9 Log2 2 weeks post vaccination with combined (ND+IB) vaccine. Two weeks post vaccination with the booster dose with ND or IB, the (AM) HI titer was 3.9 Log2 and 3 Log2 in birds of subgroup A and B respectively.
The serum neutralization results showed that the neutralizing index (NI)) 2 weeks post second dose was 6, 6 in subgroup A and B in group I respectively and it was 2.3, 7.3 in subgroup (A and B) in group II respectively, while it was 5.4, 3.5 in subgroup (A and B) in group III
respectively. 5- The protection percentage (%) after challenged
with VVNDV (Velogenic Viscerotropic NDV) 2 weeks post second vaccination was 89% - 75% in subgroup < /p>
and B in group I respectively and it was 75% in subgroup A in group II while it was 58%-34% in subgroup (A and B) in the group III respectively.