Use of live vaccines for coccidiosis control in replacement layer pullets

Coccidiosis, caused by host-specific parasites in the genus Eimeria, is a common disease in the poultry industry that produces high economic losses stemming from decreased flock performance and coccidiosis control systems. Prophylactic anticoccidials remain the prevention method of choice in the poultry industry, although drug-resistant Eimeria species and concern over drug residues in poultry products have made vaccines increasingly desirable. Many types of coccidiosis vaccines have been introduced, yet live vaccinations, either with nonattenuated or attenuated oocysts, have been commonly used in commercial poultry houses. Live Eimeria vaccination stimulates protective immunity, resulting from the first small dose of vaccinal oocysts and enhanced through cycling parasites fecal-orally. The cycling of the controlled infection with live vaccination is influenced by commercial housing techniques, especially with replacement layer pullet tiered-cage systems. This review provides an overview of coccidiosis caused by Eimeria species infecting domestic fowl and the nature of coccidial infections in commercial poultry houses, with particular attention to replacement layer hen rearing production systems in Canada and the United States.