MAREK'S DISEASE VIRUS

SUMMARY Experiments were designed to determine when to vaccinate chicks with the herpesvirus of turkeys (HVT) to obtain maximum protection against Marek's disease (MD). Vaccination one or more weeks before challenge with MD virus gave protection, vaccination after challenge gave no protection, and simultaneous vaccination and challenge gave partial protection. In commercial situations, where the time of infection with MD virus is unknown, birds should be vaccinated as early as possible, preferably on the day they hatch.