Practical immunization of chickens against coccidiosis using an attenuated strain of Eimeria tenella.

Three floor-pen trials were conducted to compare two attenuated strains of Eimeria tenella (Wis-F-96 and Wis-F-125) with the strain of E. tenella used in a commercial planned immunization program (Coccivac). Broiler cockerels were started in floor pens on new pine shavings litter. Immunizing oocysts were administered in the drinking water during the first week with total dose per bird of 175 oocysts of the control strain (Coccivac); 175, 350, or 700 oocysts of the Wis-F-125; 350 oocysts of Wis-F-96; or no oocysts (non-seeded control). The control strain was more pathogenic than the Wis-F-125 or the Wis-F-96 strains as indicated by significantly higher lesion scores 17 days after initial exposure and by loss of two birds in the control strain exposed groups. Low lesion scores and no deaths due to coccidiosis characterized the use of the Wis-F-125 strain. Flock immunity, as determined by immunity challenge, was equivalent between the control strain and the higher dosages of Wis-F-125. The Wis-F-96 strain did not adequately immunize chickens in these experiments.