Effect of live and inactivated Newcastle disease vaccines alone or in combination on humoral immune response in broiler chickens

Biosecurity and vaccination are two important tools for prevention of Newcastle disease. This study was conducted to compare the immunogenicity of live and killed Newcastle disease vaccines by measuring the hemagglutination-inhibiting antibodies in the sera of broiler chicks. For this, 270 day-old chicks (Ross) were allocated to 6 match-weighted groups (A through F). Group A was non-vaccinated control; group B received B1 and Clone 30 live vaccines by eye-drop at days 10 and 31, respectively; groups C and D were injected subcutaneously with killed vaccine at days 3 and 10, respectively; groups E and F received killed vaccine at days 3 and 10, respectively, and were also given live vaccines according to group B. From each group, four chicks were randomly selected and bled on day 3, and also 12 chicks on days 10, 17, 24, 31 and 38. Then, the collected sera were assessed by hemagglutination-inhibition (HI) test. The results show that up to day 17, there was no significant difference in HI titers among experimental groups; compared with groups which received killed vaccine only, groups given live vaccines had a significantly higher antibody level at days 31 and 38. In conclusion, live Newcastle disease vaccines, even if not repeated, give better immunity when compared to killed vaccine, and if they were used together the immune response would be stronger.