Vaccination

Decline of MDA in Progeny

MDA is protective when present at a sufficiently high titre, however due to metabolism and growth the antibody titre declines at a rate of 1 log2 VN titre every 3 to 5.5 days (broilers 3-3.5 days, broiler breeders 4.5 days and layers 5.5 days), thus 2 to 3 weeks post hatch the susceptibility of a chicken flock to an IBDV infection increases. MDA protects chickens against field infection but also neutralises live vaccines resulting in vaccine failure. Knowing the source of day old chickens and determining the level of circulating MDA is critical to the implementation of an effective live vaccination program.