Ovine coccidiosis: studies on the pathogenicity of Eimeria ovinoidalis and E. crandallis in conventionally-reared lambs, including possible effects of passive immunity.

No pathogenic effect was detected in lambs when 10(4) oocyts of each species were inoculated before 72 h of age. At 4 weeks of age the combined inoculum caused diarrhoea and weight loss, the severity being roughly proportional to the size of the inoculum. Even 1000 oocysts of each species caused diarrhoea; the pathogenic effect was attributable mainly to E. ovinoidalis. Hyperimmunization of ewes during pregnancy (by repeated inoculation of massive doses of oocysts) reduced the effects of oocyst inoculation in their progeny. Levamisole administration during pregnancy increased the birthweight of lambs.