A field study on the significance of vaccination against infectious bursal disease virus (IBDV) at the optimal time point in broiler flocks with maternally derived IBDV antibodies.

The right strategy for infectious bursal disease (IBD) control and its success rate under field conditions depends on hygiene management, IBD field pressure, level and variation in maternally derived IBD antibodies, and the IBD vaccine strains to be used. Usually, standard vaccination programmes are used, which are not always adapted to the specific conditions on the farm and to the immune status of chickens. Employing the "Deventer formula" may help to estimate the optimal time for vaccination for a specific flock based on the maternally derived antibody level, its variation, the genetic background of the chicken, and the IBD vaccine strain.