Success and failure: The role of relative humidity levels and environmental management in live Eimeria vaccination of cage-reared replacement layer pullets

Contrary to the traditional view that layer flocks housed in conventional cages are unlikely to suffer coccidiosis caused by Eimeria species, this enteric disease has become an emergent issue. Coccidiosis outbreaks in layers are frequently associated with the failure to develop protective immunity at a young age. Layer hens housed in cages are usually sourced from replacement layer pullets housed in similar cages in the rearing barn. Live coccidiosis vaccines administered to young chicks provide a small dose of vaccine oocysts that infect and replicate within the vaccinated birds, resulting in the release of progeny oocysts into the rearing environment; these oocysts must become infective (i.e., sporulate) and then reinfect the partially immune birds in order for the vaccine to generate complete protective immunity. Three factors are needed for successful oocyst sporulation: temperature (4 to 37 degrees C; optimal 29 degrees C), oxygen access, and adequate RH. The purpose of this study was to assess the degree of protective immunity elicited by birds spray-vaccinated with a live coccidiosis vaccine at the hatchery. During the critical period for oocyst sporulation and cycling, RH levels decreased to 13 to 19%, resulting in inadequate oocyst cycling and minimal protection against homologous challenge at 6 and 12 wk of age. This vaccination failure highlights the need to monitor RH in the barn and modify the barn environment so that conditions promote, rather than impede, the success of live coccidiosis vaccines.