PATHOGENICITY OF ATTENUATED INFECTIOUS-BRONCHITIS VIRUSES FOR OVIDUCTS OF CHICKENS EXPOSED IN OVO

A fixed effects, completely randomized factorial design was used to st udy tile effect of infectious bronchitis virus (IBV) inoculation at tw o different exposure ages and three postinoculation (PI) durations on chick oviduct pathology. Maternal antibody-positive chicken embryos at 18 days of embryonation (ED) and, newly hatched chicks were inoculate d with an IBV vaccine (V-IBV) or with an IBV vaccine that had been ser ially passaged 21 times in chick kidney tissue culture (P-IBV). Hatcha bility of eggs inoculated with V-IBV at 18 ED was significantly lower (27%) than eggs that were not inoculated with IBV or were inoculated w ith P-IBV (45-58%, P < 0.01). Chicks from all treatment groups survive d to 5 days after hatch. Pathologic changes in the oviduct were evalua ted at 9, 18, and 27 days PI by light microscopy. Inoculation of V-IBV and P-IBV in the presence of maternal antibodies did not result in an y oviduct pathology at 9, 18, and 27 days PI. Respiratory clinical sig ns, however, were observed in 61% and 5% of chicks inoculated with V-I BV at 18 ED and at hatch, respectively. Respiratory clinical signs wer e not observed in control birds, birds inoculated with P-IBV at 18 ED, or birds inoculated with P-IBV at hatch.