Practical aspects of estimation of optimal time for vaccination of chicken against IBD with use of "Deventer formula".

One of the most commonly applied vaccination strategies against chicken infectious bursal disease (IBD) is the use of live vaccines at the optimal time estimated with the use of Deventer formula. The present study investigated the impact of different factors on maternally derived antibodies decline and therefore on the vaccination schedule against IBD. Our results suggest that blood collection from birds older than 3 days is more reliable in order to estimate the optimal date for IBD vaccination, due to disturbances in yolk sac resorption early after hatch.