Coccidiosis is a protozoan parasite that may produce clinical symptoms in calves from 1 month to 1 year of age. The major damage to calves is the result of the rapid multiplication of the parasite in the intestinal wall and the subsequent rupture of the cells of the intestinal lining. Several stages of multiplication occur before the final stage, the oocyst (egg), is passed in the feces. Oocysts are extremely resistant to environmental stress and are difficult to remove from the environment completely. Oocysts must undergo a final process called sporulation before they are infective again. Oocysts frequently contaminate feed and water. When the sporulated oocysts are ingested by calves, they start their life cycle over in the new host. In mild cases, calves only have watery diarrhea, but in most cases, blood is present in the feces. Straining, along with rapid dehydration, weight loss and anorexia (off feed), may be evident.