Five trials were carried out with more than 15, 000 chickens, including approximately 10, 000 birds inoculated with Marek's disease vaccine (Deptavac-HVT). Each trial lasted for 180 days.
The disease broke out in 7.5% of the vaccinated birds and 14.4% of the unvaccinated control ones. The rate of decrease in outbreak of the disease in the vaccinated birds was 48.1%. Death and culling occurred from a variety f causes, including weakness accidental death, cannibalism, Marek's disease, leucosis, and chronic respiratory diseease.
There was no significant difference in positive rate for gel-precipitating antibody against Marek's disease, mean titer of neutralizing antibody against infectious bronchitis virus, or positive rate for agglutination againstMycoplasma gallisepticunzbetween the vaccinated and control groups. When some vaccinated birds were subsequently inoculated with killed or live Newcastle disease vaccine 2 to 4 times during a period from 4 to 143 days of age no hemagglutinatio-ninhibiting antibody response to this vaccine was suppressed in any of 4 vaccinated groups.
