Abstract

In this study infectious bursal disease (IBD) vaccinations were evaluated against very virulent IBD (vvIBDV) challenge and were compared. A total of 120-day-old white Leghorn SPF chickens were divided into 6 groups (each was 20 birds). Two groups were vaccinated on either day 1 with an immune-complex vaccine. The second groups were vaccinated at days 9 and 14 of age using intermediate and intermediate plus IBD vaccines, respectively the balance groups are controls. All vaccines were administered according to the manufacturer's instructions. The challenge was conducted on the 16 days of age using 105 EID50 /0.1 ml of a vvIBDV strain via the oculonasal route. The antibody immune response was monitored in all groups at 14, 21, 28, and 35 days of age. The performance, bursal gross lesions, challenge virus detection, and bursal histopathology were evaluated in vaccinated non challenged and vaccinated challenged birds at days 21 and 28 of age. All vaccinated groups were protected against the vvIBDV challenge compared to 40% mortality in the challenge control group. Both the immune-complex and live attenuated IBD vaccine groups showed similar bursa body weight (BB) ratios compared to the negative control group. The immune-complex vaccinated groups antibody titers were significantly higher except on 28th day of age. Upon challenge, the intermediate/intermediate plus vaccinated challenged group showed higher antibody titers at 21 and 35th with the challenge virus detection and quantification on day 28. The immune-complex vaccinated challenged group developed milder bursal histopathology signs but no differences between the 2 vaccine programs were seen. It can be understandable, the use of either immune-complex vaccine at day-old or early vaccination with intermediate followed by intermediate plus live attenuated IBD vaccines induced protective antibody titers and protect chickens against an early vvIBDV challenge. The suggested schedules need further evaluation in commercial broilers with maternal derived IBD antibodies to simulate field conditions.