Protection of laying chickens against the Canadian DMV/1639 infectious bronchitis virus infection through priming with heterologous live vaccine and boosting with heterologous or homologous inactivated vaccine

The emergence of the Canadian Delmarva (DMV)/1639 infectious bronchitis virus (IBV) type strains was asso-ciated with egg production disorders in Eastern Canadian layer operations. While developing vaccines for novel IBV variants is not typically a reasonable approach, the consideration of an autogenous vaccine becomes more appealing, particularly when the new variant presents significant economic challenges. The current study aimed to compare the efficacies of two vaccination programs that included heterologous live priming by Massachusetts (Mass) and Connecticut (Conn) type vaccines followed by either a commercial inactivated Mass type vaccine or a locally prepared autogenous inactivated DMV/1639 type vaccine against DMV/1639 IBV challenge. The pro-tection parameters evaluated were egg production, viral shedding, dissemination of the virus in tissues, gross and microscopic lesions, and immunological responses. The challenge with the DMV/1639 caused severe conse-quences in the non-vaccinated laying hens including significant drop in egg production, production of low -quality eggs, serious damage to the reproductive organs, and yolk peritonitis. The two vaccination programs protected the layers from the poor egg-laying performance and the pathology. The vaccination program incor-porating the autogenous inactivated DMV/1639 type vaccine was more effective in reducing vial loads in renal and reproductive tissues. This was associated with a higher virus neutralization titer compared to the group that received the commercial inactivated Mass type vaccine. Additionally, the autogenous vaccine boost led to a significant reduction in the viral shedding compared to the non-vaccinated laying hens. However, both vacci-nation programs induced significant level of protection considering all parameters examined. Overall, the findings from this study underscore the significance of IBV vaccination for protecting laying hens.