PROTECTION AGAINST COCCIDIOSIS IN OUTBRED CHICKENS ELICITED BY GAMMA-IRRADIATED EIMERIA-MAXIMA

In an effort to develop an attenuated coccidiosis vaccine against cocc idiosis, we exposed Eimeria maxima oocysts to an optimum dose of gamma irradiation (II kRad) that does not affect sporozoite invasion of the intestinal mucosa but does prevent asexual parasite development. Irra diated E. maxima oocysts were suspended in gelatin slabs and placed in battery cages for ingestion by I-day-old chickens. Separate groups of chickens were given gelatin slabs containing nonirradiated E. maxima oocysts or were inoculated pet os with either irradiated or nonirradia ted E. maxima oocysts. Chickens infected with irradiated or nonirradia ted oocysts by either oral inoculation or gel delivery showed a dose-d ependent protection against weight loss associated with E. ma;rima cha llenge compared with unimmunized controls. In general, nonirradiated o ocysts elicited protective immunity at lower immunization doses compar ed with irradiated oocysts. These experiments were extended to a floor pen study wherein 1-day-old male and Female broiler chickens were giv en irradiated or nonirradiated E. maxima oocysts in gelatin slabs in h atching boxes and challenged at 4 wk of age. A significant reduction ( P < 0.05) in lesion scores was observed for chickens immunized with ei ther irradiated or nonirradiated oocysts compared with unimmunized con trols. Although no significant difference (P > 0.05) was observed in w eight gain between these groups, both male and female chickens inocula ted with irradiated E. maxima oocysts showed about a 10% greater weigh t gain than unimmunized controls, For both male and female chickens, a verage weights at challenge were greater in groups that were immunized with 17-kRad-irradiated E, maxima oocysts compared with those animals immunized with nonirradiated oocysts.