FIELD EFFICACY OF DIFFERENT VACCINES AGAINST INFECTIOUS BURSAL DISEASE IN BROILER FLOCKS

A field study was performed to determine the efficacy of three commercially available vaccines against infectious bursal disease (IBD) in commercial broilers raised in a high IBD virus (IBDV) risk area. Live attenuated intermediate and intermediate plus vaccines were used in four flocks. Birds were vaccinated orally at the estimated vaccination time. Three broiler flocks were vaccinated subcutaneously with a turkey herpesvirus (HVT)-IBD vector vaccine at one day old. Evaluation of the efficacy of different vaccines was focused on humoral immune response, bursa/body weight (B/Bw) ratio, molecular detection of IBDV in ileocaecal tonsils and bursa of Fabricius, and production parameters. The serological results showed that although the uptake of all three vaccine strains was confirmed in the lymphoid organs, no significant antibody response to vaccination was detected in flocks vaccinated with intermediate and intermediate plus vaccines. A significant increase in antibody titres detected in flocks vaccinated with the vector vaccine indicated its ability to induce an immune response in birds with a high level of maternally derived antibodies. Observations obtained in this field trial did not confirm the expected reduction of the B/Bw ratio in flocks vaccinated with less attenuated vaccines. No significant differences were observed between birds vaccinated with the vector vaccine and those immunised with the intermediate plus vaccine. Very virulent IBDV was confirmed in the flock vaccinated with the intermediate vaccine. The infection induced reduced B/Bw and moderate mortality but did not affect the production parameters. Field infection was not detected in broilers vaccinated with the intermediate plus vaccine and the vector vaccine.