B. Newcastle Disease

The main objective of ND vaccination is to protect the parents against the adverse effects on production associated with field challenge. Strains of ND known to occur in GB at present are of very low virulence. Ireland (north and south) is considered to be free of ND. Where there is a perceived risk then broiler parent chickens will usually be vaccinated 2-3 times during rear using a live vaccine (most commonly in drinking water). This is followed with an oil-adjuvant vaccine at 17-18 weeks of age (usually combined with the IBD vaccine). The serological data summarized as geometric mean titre for each of 741 house flocks (305 in rear, 436 in lay, 9992 individual sera) are shown in figure 3.2. The pattern is very similar to that of IBD.

A smaller number of tests (68 groups, 1457 sera) have been carried out using an Elisa test (IDEXX). Most of these were routine samples (not related to disease investigation). Mean titre groups were generally higher than the HI-GMT's which we would expect (Figure 3.3). Some individual sera reacted so strongly that they exceeded the limits of the plate reader. These were designated titre group 13 for the purpose of calculating the mean titre.