Safety and efficacy of in ovo administration of infectious bursal disease viral vaccines

In ovo vaccination against Marek's disease virus and infectious bursal dise ase virus (IBDV) in commercial broilers in the United States is common. Lit tle information exists as to the safety and efficacy of intermediate IBDV v accines given in ovo. Experiments were initiated to determine the safety an d efficacy of three commercially available live intermediate IBDV vaccines by in ovo route. Commonly used vaccines were given at 18 days of embryonati on to specific-pathogen-free (SPF) broiler embryos (first- and second study ) or to commercial broiler embryos (third study) that had maternal antibody against IBDV. When any of the antigenic standard vaccines was given at ful l dose to SPF embryos, embryonic and 3-wk posthatch mortality increased. Va ccines also caused significant microscopic lesions in the bursa of Fabriciu s at 1 and 3 wk posthatch. In contrast, there was no adverse effect on embr yonic or posthatch mortality when vaccines were given at half dose to SPF o r commercial broiler embryos. However, significant microscopic lesions were evident at 1 and 3 wk posthatch in the bursae of SPF embryos given the vac cines at half dose. When vaccines were given at half dose to commercial bro iler embryos, lesions were evident at 1 but not 3 wk of age. In the third s tudy, in ovo vaccinated chickens were challenged with either a virulent sta ndard (APHIS) or antigenic variant (variant E) IBDV virus at 3 wk of age. A ll vaccines produced at least 87% protection against the standard and 60% p rotection against the variant challenge IBDV, as measured by bursal weight to body weight ratios. This study was the first to examine the safety and e fficacy of the three commonly used intermediate IBDV vaccines given in ovo in protection against standard and antigenic variant IBDV challenge viruses .