Studies On Embryonal Vaccination Of Marek's Disease

More systematic studies have been made of the optimum way of embryonal vaccination, the effect on hatchability and strong chick rate of embryonally vaccinated chickens, and the affection upon the development and immunological protection of embryonally vaccinated chickens challenged with Marek's disease virus (MDV ) by means of innoculating Beijing White 904 chicken eggs on the 18th embryonation day with turkeys herpesvirus (HVT). The results show that embryonal vaccinations were effective by any of the three ways (through the halfway on the long axis of egg, through the large end of the egg, or by inserting in amniotic sac) with the large end of the egg obtaining the optimum effect, which did not affect the hatchability and the strong chick rate, and helpful for mechanical and automatic operation. Early development of chicken lymph organs was obviously accelerated by embryo vaccination with HVT vaccine and the growth of embryonally vaccinated chickens is much faster than that of unvaccinated chickens at the same raising conditions. The embryonally vaccinated chickens were most effective for preventing MD tumor formation when challenged at the same day. The post — hatched chickens obtained strong immunological protection on the 15th day, while the embryonally vaccinated chickens reveal immunological protection only after the 3rd day of post —hatch.