Efficacy of live NDV vaccine simultaneously vaccinated with recombinant HVT-NDV vaccine on early protection against Newcastle disease virus challenge

Abstract

The objective of this study was to determine the efficacy of the recombinant herpes virus of turkey-Newcastle
disease virus (rHVT-NDV) vaccine against Newcastle disease virus (NDV) challenged in 14 days old broiler chickens.
One hundred chickens were divided into 5 groups of 20 chickens each. Group 1 chickens received live NDV vaccine
via the intra-nasal route. Group 2 chickens received rHVT-NDV vaccine by subcutaneous injection. Group 3 chickens,
received both live NDV and rHVT-NDV vaccine. Groups 4 and 5 chickens did not receive any vaccine and served as
positive and negative control groups. At 14 days old, all the chickens in Groups 1-4 received virulent NDV challenged
by oral drop. The results revealed that the mortality rate of chickens in Groups 1-5 was 50%, 70%, 0%, 100% and 0%,
respectively. At 24 days old, the body weight of the surviving chickens in group 1 was the lowest, while the surviving
chickens of Groups 2, 3 and 5 were not significantly different (p > 0.05). At 14-day old, antibodies against NDV was
detected by hemagglutination-inhibition (HI) test showing that Group 3 had the highest antibody titer level, followed
by Group 1, while Group 2 showed a low HI titer similar to non-vaccinated groups. HI test and enzyme-linked
immunosorbent assay (ELISA) at 24 days old (10 DPI), increased significantly when compared to those of at 14 days
old. In conclusion, the chickens that received live NDV vaccine and was simultaneously vaccinated with rHVT-NDV
vaccine at 1 day old, had a higher protection rate than chickens which received either live or recombinant vaccine alone.