Development of immunity in broilers continuously exposed to Eimeria sp.

A series of experiments was conducted to determine the time required to induce absolute immunity to three species of Eimeria in young broiler chickens continuously exposed to the parasite. Acquisition of immunity was measured by cessation of oocyst production in each bird. Initial experiments were performed in broilers beginning at age 7 days with continuous oocyst administration for 28 days with E. tenella, E. maxima, or E. acervulina. Evaluation of oocyst production demonstrated a major decline in oocyst output of E. maxima and E. tenella by 2 weeks, with cessation by 25 days. Exposure to E. acervulina caused cessation of oocyst production by day 16. To study whether chickens of different ages varied in their capacity to immunize within this time frame, 1-day-old birds also were studied. For E. tenella, exposures also were initiated in 14- and 21-day-old birds. This study demonstrated that regardless of the age of the broiler, all were capable of establishing complete protective immunity to E. tenella, E. maxima, and E. acervulina under continuous exposure within 25, 24, and 16 days, respectively.