Immunization of young chickens by trickle infection with Eimeria tenella.

Immunization of chickens was attempted with low levels of Eimeria tenella oocysts (50 oocysts per day) over the first 1 or 2 weeks of life--the "trickle infection" (TI) method. When chickens were immunized by TI at 0-13 days of age, no cecal lesions and a reduced number of oocysts in ceca were observed after challenge at 17 days of age. TI at 0-6 days of age conferred better protection against challenge with E. tenella than did TI at 7-13 days. However, cecal lesions were observed in almost all of these chickens. These findings indicated that TI for 2 weeks (0-13 days of age) provided better immunity than TI for 1 week (0-6 or 7-13 days of age).