| Summary |
Various Newcastle disease (ND) vaccination programs were tested for their protection efficacy. In trial 1, SPF chicks were vaccinated with an attenuated or inactivated ND vaccine at 4-day-old, then boosted again with an attenuated or inactivated ND vaccine at 7 days of age or 14 days of age. All vaccinated groups showed a good protection rate (80-100%) when they were challenged with a virulent ND virus at 5-week-old. In trials 2 and 3, several groups of broilers with high maternal antibodies (geometric mean hemagglutination-inhibition antibody titer was 1:84.5-1:135 at 4-day-old) were simultaneously immunized with an attenuated and an inactivated ND vaccine at 4 days of age, and then revaccinated with an attenuated ND vaccine at 17-day-old. Other groups of broilers were first vaccinated with a live vaccine at 4-day-old, revaccinated with an inactivated vaccine at 14-day-old, and then boosted again with a live vaccine at 17-day-old. Good protection rate (80-100%) was achieved in both groups when they were challenged at 5-week-old. When they were challenged at 3-week-old and 4-week-old, the latter broiler groups had a significantly higher protection rate (100%) than the formal broiler groups (50-80%)(p<0.05).
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