The efficacy of commercially available recombinant herpes virus of turkeys-infectious bursal disease virus (rHVT-IBD) vaccines in broiler chickens derived from an IBDV-vaccinated breeder flock at 30-weeks of age (Trial 1) and 60-weeks of age (Trial 2) was studied. Specific-pathogen-free (SPF) white leghorn chickens, free of maternal antibodies against IBDV, were used as controls.
Broilers and SPF leghorns were vaccinated subcutaneously in the neck at one-day of age with Company A rHVT-IBD or Company B rHVT-IBD vaccines and were placed in isolators. On day post vaccination (DPV) 10, 14, 18, 22 and 26, vaccinated and unvaccinated broilers and SPF leghorns were bled and challenged via the conjunctiva sac route with reference strains ST-C, Delaware variant E (DelE), or contemporary field isolates DMV/5038/07 or FF6.
IBDV serum antibodies were detected to varying degrees depending on the commercial ELISA kit used. ELISA A and C kits more readily detected rHVT IBDV vaccine induced (active) serum antibodies compared to ELISA kits B and D. Bursa/bodyweight ratios were not consistently useful as a tool for assessing IBDV challenge in broiler chickens with IBDV maternal antibodies.
Bursa/bodyweight (B/BW) ratios were more useful for assessing protection against IBDV challenge in SPF leghorns. Microscopic lesion assessment of the bursa was useful for assessing IBDV challenge in both rHVT-IBD-vaccinated broiler and SPF leghorn chickens. rHVT-IBD vaccines, in general, induced greater protection with increasing age of the chicken.
Based on bursal microscopic lesion assessment, Company A rHVT-IBD vaccination of SPF leghorns induced protection by 18 DPV and continued to protect on 22 DPV and 26 DPV in Trials 1 and 2. Company B's rHVT-IBD vaccine induced protection of SPF leghorns by 18 or 22 DPV in Trial 1, depending on the IBDV used for challenge. However, the onset of protection was delayed until 22 or 26 DPV in Trial 2.rHVT-IBD vaccination of broiler chickens with either commercial vaccine was not as effective as was observed in SPF leghorns, based on bursal microscopic lesion assessment
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