Coccidiosis is caused by one-celled parasites that invade the intestinal tract of animals. There are many species of coccidia. Two, Eimeria zurnii and Eimeria bovis , are usually associated with clinical infections in cattle. Coccidiosis has been observed in calves 3 weeks of age and older, usually following stress, poor sanitation, overcrowding or sudden changes of feed. It often occurs in calves 7 to 14 days after they are moved from the calving lots onto pasture.
Clinical coccidiosis is diagnosed by finding significant numbers of parasites in the feces.
The results of the fecal examination must be related to the clinical signs and intestinal lesions. Occasionally, clinical coccidiosis will be present with bleeding and very few parasites in the fecal material. Laboratory examination of sections of the intestine may be required for diagnosis. A typical sign of coccidiosis in young calves is diarrhea with fecal material smeared over the rump as far around as the tail will reach. This may or may not contain blood.