Infectious Bursal Disease Emulsified Vaccine: Effect upon Neutralizing-Antibody Levels in the Dam and Subsequent Protection of the Progeny

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Abstract
Two groups of White Leghorn hens, 1 vaccinated at 2 wk against infectious bursal disease (IBD) and the other free of antibodies [Ab] against IBD virus (IBDV), were vaccinated at 16 wk old with a suspension or a multiple emulsion of killed IBDV. Untreated hens from each flock were kept as controls. All birds were bled periodically for 50 wk after vaccination. Fertile eggs were collected 25 wk after vaccination. Ab levels in the yolk were determined. Chickens hatched from the fertile eggs were bled and challenged with IBDV at weekly intervals to determine the persistence of serum Ab and resistance to bursal atrophy. Hens re-vaccinated with the emulsified vaccine and the chickens derived from them had the highest neutralizing and most uniform titers and complete protection in the chickens lasted to 4 wk. Of 5 chickens, 2 were still protected against challenge at 5 wk of age. In chickens derived from hens re-vaccinated with a suspension of killed virus, protection was always partial, being in close relation with age; 4 of 5 chicks were protected in the 1st wk of age and the rate of protection diminished to only 1 of 5 by 5 wk of age. Chickens obtained from unrevaccinated hens were protected only during the 1st wk of life.