Protective immunity to infectious bronchitis in broilers vaccinated against Marek's disease either in ovo or at hatch and against infectious bronchitis at hatch

Two experiments were conducted using commercial broiler chickens to determi ne if Marek's disease (MD) vaccines HVT/SB-1 and HVT plus CVI-988 given eit her in ovo or at hatch adversely affected the efficacy of infectious bronch itis (IB) vaccines (Ark and Mass serotypes) given by eyedrop on the day of hatch. Nonvaccinated negative controls and controls that received only IB v accines were included in each study. Birds were challenged with either infe ctious bronchitis virus (IBV) Mass-41 or IBV Ark-99 on either day 26 or 27 of age. Protection was assessed 5 days post-IBV challenged by virus isolati on from the trachea. The day of hatch mean antibody titer to IBV was 12,668 +/- 4704 and 2503 +/- 3243 by enzyme-linked immunosorbent assay in experim ents 1 and 2, respectively. In each study, nonvaccinated controls had a sig nificantly higher (P less than or equal to 0.05) incidence (88%-100%) of IB V challenge virus isolation than did controls vaccinated for IB but not for MD. Analysis of data from both studies showed that protection to IB in gro ups that received only IB vaccines at hatch ranged from 55.0% to 77.3%, whe reas protection to IB in groups receiving both MD and IB vaccines ranged fr om 50.0% to 95.5%. In both experiments and within IBV challenge serotype, b roilers given MD vaccines (in ovo or at hatch) and IB vaccines at hatch had protection rates to IBV challenges that were not significantly less (P les s than or equal to 0.05) than IB protection rates of groups that received o nly IB vaccines at hatch. Analysis of these data shows that administration of high-titered MD vaccines either in ovo or at hatch did not affect the ef ficacy of an IB vaccination (serotypes Ark and Mass) given by eyedrop at ha tch.