Pathogenicity of Eimeria acervulina in Light and Heavy Coccidial Infections

Two-week-old cockerels (124 birds) scored 0, +1, +2, +3, and -4 for lesions produced by Eimeria acervulina respectively gained 55, 51, 44, 35, and 38 grams. In a typical controlled experiment, four-week-old cockerels which scored 0, +1.2, +2.8, and +3.8 respectively gained 252, 251, 236, and 167 g in the first week postinoculation. Respective gains four weeks postinoculation were 780, 813, 776, and 681 g. Thus, +1 and (possibly) +2 lesions, commonly recognized as E. acervulina coccidiosis in field cases, should probably be diagnosed as coccidiasis. Heavy infection, sometimes overlooked because of coalescence of lesions, produces marked reduction in growth rates. Suppression of growth rates may appear in infected birds 3-4 weeks postinfection, but they are most apparent one week after inoculation.