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 emerging health issue, according to K.R. Price and colleagues at the University of Guelph in Canada. They report that coccidiosis outbreaks in layers are frequently associated with the failure to develop protective immunity at a young age.

In a paper in the current issue of Journal of Applied Poultry Research, they state that laying 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°C; optimal 29°C), oxygen access and adequate relative humidity.

The Guelph study aimed 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, relative humidity levels decreased to 13 to 19 per cent, resulting in inadequate oocyst cycling and minimal protection against homologous challenge at six and 12 weeks of age.

This vaccination failure highlights the need to monitor relative humdity in the barn and modify the barn environment so that conditions promote, rather than impede, the success of live coccidiosis vaccines, concluded Price and colleagues.

Reference

Price K.R., M.T. Guerin and J.R. Barta. 2014. Success and failure: The role of relative humidity levels and environmental management in live Eimeria vaccination of cage-reared replacement layer pullets. J. Appl. Poult. Res. 23(3):523-535. doi: 10.3382/japr.2014-00989

October 2014