[Study of the effect of some of the vaccination plans applied in Bulgaria against Newcastle disease].

Comparative studies were carried out on the effect of the vaccination of broilers against Newcastle disease with La Sota strain through the single application in the drinking water on the 21st day and the newly introduced vaccination at the age of four days, using the spray method, as well as the combined method--spray vaccination on the fourth day and giving the vaccine twice on the 21st day. It was found that the last method confers better immunity and higher immunity against the disease as compared to offering the vaccine only once on the 21st day.