Passive immunization of chicks against Newcastle Disease by administration of egg yolk from hyperimmunized hens

The water soluble livetin fraction was extracted from the yolk of eggs laid by hens hyperimmunised with Newcastle Disease Virus (N.D.V.). This fraction, when injected intramuscularly into 14 day old chicks, was eliminated at a slower rate than it was from 7 week old birds. A combination of yolk fraction and vaccine, when injected into 21 day old chicks, conferred better protection against contact challenge with N.D.V. than did the vaccine alone. Injection of the yolk fraction alone gave the best protection. When 21 day old chicks were treated twice at 7 day intervals with yolk, yolk and vaccine or vaccine alone and challenged by contact at the time of the first treatment, a significantly better protection was observed than in the untreated control group. Aluminium stearate, paraffin oil or chlorbutanol, when mixed with the yolk fraction, retarded its rate of absorption from the site of injection. Though H.I. antibody persisted longer in the circulation of chicks given these mixtures, the latter did not give better protection against N.D.V. than the yolk fraction without any additives.