Immunity to Newcastle disease in fowl of different breeds, primarily vaccinated with commercial inactivated oil‐emulsion vaccines: A laboratory experiment

Fowl were primarily vaccinated with commercial inactivated oil emulsion (IOE) Newcastle disease (ND) vaccines and immunity was established by both determination of haemagglutination inhibiting (HI) antibodies and by challenge, over periods similar to the economic life span of the birds. The effect of level of maternal antibodies, route of vaccine administration, and vaccine dose on the vaccination results were studied. In one experiment, immunity provoked by vaccination with IOE vaccine was compared with that obtained by vaccination with live vaccines. Vaccination by the subcutaneous route induced a significantly stronger HI response than intramuscular vaccination. Also the vaccine dose per bird and the level of maternal antibodies influenced the vaccination results. In both brown layer and White Leghorn (WL) hens a strong immunity was induced up to at least 45 and 78 weeks of age respectively, by vaccination with IOE vaccine at 6 weeks of age. Also WL hens primarily vaccinated with IOE vaccine at 70 weeks of age, responded with high levels of HI antibodies, which persisted for at least 39 weeks. However, immunity in meat type fowl vaccinated at 6 weeks of age was poor. Following subcutaneous vaccination of one-day-old broilers with high maternal antibody titres with one dose of IOE vaccine per bird, immunity during the fattening period was at an insignificantly lower level than in birds vaccinated with live vaccine at 7 days of age. Twofold vaccination with IOE vaccine at one day old and 18 weeks of age of meat type fowl with high maternal antibody titres provoked a moderate immunity up to at least 55 weeks of age.(ABSTRACT TRUNCATED AT 250 WORDS)