Minimum Infectious Dose Determination of the Arkansas Delmarva Poultry Industry Infectious Bronchitis Virus Vaccine Delivered by Hatchery Spray Cabinet

SUMMARY The Arkansas Delmarva Poultry Industry (ArkDPI) infectious bronchitis virus (IBV) vaccine is effective when administered by eye drop, where the vaccine virus is able to infect and replicate well in birds and is able to induce protection against homologous challenge. However, accumulating evidence indicates that the ArkDPI vaccine is ineffective when applied by hatchery spray cabinet using the same manufacturer-recommended dose per bird. For this study, we aimed to determine the minimum infectious dose for the spray-administered ArkDPI vaccine, which we designate as the dose that achieves the same level of infection and replication as the eye drop–administered ArkDPI vaccine. To this end, we used increasing doses of commercial ArkDPI vaccine to vaccinate 100 commercial broiler chicks at day of hatch, using a commercial hatchery spray cabinet. The choanal cleft of each bird was swabbed at 7 and 10 days postvaccination, and real-time reverse-transcriptase PCR was performed. We observed that the level...