Maternally derived antibody--effect on susceptibility of chicks to infectious bursal disease.

Levels of infectious bursal disease (IBD) antibody in young chicks from infected parents were measured using the quantitative gel diffusion precipitation test (QGPT). The decay of maternally derived antibody was approximately linear with a half life of about 4 days. Groups of chickens from this flock were inoculated with infectious bursal agent. All chicks which were inoculated at 8 days of age were resistant to infection and all inoculated at 17 days of age were susceptible. About half of the chicks inoculated at 14 days of age were susceptible to infection. One hundred chicks hatched from 10 hens showed considerable variation in their QGPT titres. Precipitin levels in one-day-old chicks from the same parent showed little variation, and were usually one or 2 log(2) lower than their dams.