Pathogenicity of the coccidium Eimeria crandallis in laboratory lambs.

Ten colostrum-deprived, coccidia-free lambs were reared artificially in indoor cages. At 4 weeks of age they were allocated to 5 groups of 2: Groups 1-3 received 10(4), 10(5) and 10(6) sporulated oocysts of Eimeria crandallis/lamb respectively, each as a single inoculum. Group 4 lambs received daily doses increasing over a 4-week period. Groups 1-3 showed diarrhoea and weight loss from about day 14, followed by slow recovery from about day 30. The diarrhoea was accompanied by a wave of oocyst output and a reduction in serum albumin and plasma alkaline phosphatase activity. One lamb in group 4 died of an unrelated condition on day 15; the other showed no clinical effect of the oocyst inoculations and its oocyst output was related only to the first week or two of inoculation. Lambs in Group 1 showed no clinical effect or oocyst output following challenge with 10(6) oocysts on day 28. E. crandallis showed high pathogenicity and immunogenicity. Its pathogenicity was not closely related to infecting dose within the range 10(4)-10(6).