The importance of uniform IBD antibody levels in day old chicks

Use of the Deventer Calculator

Vaccination programmes for infectious poultry diseases such as IB, ND or TRT are recognised as offering a certain amount in timing flexibility.  However, with Gumboro vaccine, administration time is more critical. Where Gumboro disease is a threat, one wants to vaccinate chicks as soon as possible.  For vaccines to be effective, the MDA level needs to have declined sufficiently to enable full immune stimulation as explained in the graph below. This is where the specifically designed Deventer method of calculation can be used to help demonstrate the optimal time for Gumboro vaccination.

During the first 21 days of life, chick maternal antibodies can be seen to decline at a steady rate within the flock. The starting level and uniformity is usually dependent on the success of breeder vaccination processes. The red arrow on the graph above, demonstrates when the antibody level has fallen in a sufficient number of birds to enable an active immune response from Nobilis D78 vaccine administration. An active immunity will then be stimulated in those susceptible birds providing protection against IBD. If the vaccination were to be administered prior to this date, there would be a number of chicks that would fail to respond owing to the presence of maternal antibodies.

This method of calculation as described, is based on the titre level when a certain percentage of the flock can be successfully vaccinated. Based on field experience this formula uses 75% as a default percentage. To obtain reliable prediction dates a minimum of 18 day old chicks per house has to be sampled.