A comparison of immune responses of broiler chickens to different methods of vaccination against Newcastle disease.

One-day-old broiler chicks from 4 groups of broiler breeder chickens were immunized by different methods of vaccination: 1) aerosol; 2) intratracheal; 3) drinking water; or 4) unvaccinated. The breeder flock from which the chicks were derived was vaccinated by one of the following methods: 1) a single injection of an oil-emulsion Newcastle disease virus (NDV) vaccine; 2) two vaccinations with oil-emulsion NDV vaccine; 3) vaccination with a live NDV vaccine; and 4) unvaccinated controls. Aerosol vaccination induced higher serologic responses than water and intratracheal vaccination, as well as giving the highest levels of protection against challenge. Mortality ranged from 20% to 66% in all eight groups of birds vaccinated intratracheally and challenged at 6 weeks of age. Results of challenge tests, in agreement with results of HI tests, further demonstrated that intratracheal vaccination at one day of age does not elicit a satisfactory immune response in birds with a maternal antibody titer of 15 or higher.