RESUMO
Chickens, of various age groups, were vaccinated against Newcastle disease by spray vaccination with an experimental vaccine, designated V5K7E1. Aerosol spraying of 3-days-old chicks having a high titre of maternal antibodies failed to induce any obvious stimulation of haemagglutination-inhibiting antibodies. The chicks, when challenged 2 and 3 weeks after vaccination, were fully protected, but protection was inadequate when they were challenged 4 to 7 weeks after vaccination. Spray vaccination of 1-day-old specific-pathogen-free chicks resulted in the presence of antibodies at 7, 14 and 21 days. Subsequently the levels of antibodies declined progressively. The chicks resisted challenge up to 42 days after vaccination. Maternally immune chicks spray - vaccinated for the first time at 14 days showed a significant increase in antibodies and remained healthy when challenged at 10 weeks of age. Booster spray vaccination at 21 days of age subsequent to primary spray vaccination at 3 days of age, induced an anamnestic rise in antibody titre that persisted at protective levels for at least 66 days. Similarly, spray vaccination at 28 days, following administration of vaccine in the drinking water at 14 days, gave rise to high antibody titres which persisted for at least 70 days. In field trials, spray vaccination at the age of 3 days or 14 days provoked little or no apparent respiratory disturbance and was followed by an average mortality of 0.9% and 1.4% respectively.
