Coccidiosis is caused by microscopic protozoa (one-celled organisms). Coccidiosis is an important, contagious disease caused by several species of coccidia. Transmission occurs via ingestion of oocysts in contaminated feed or water. Overcrowding and stress can contribute to a coccidia outbreak. Clinical signs are bloody diarrhea (although this may not be present at all), weakness, weight loss, staring, lack of appetite and death. Aprolium (Corid) may be used as a treatment although it is better to prevent the disease then to wait until an outbreak occurs. A supplemental Vitamin B Complex should be administered when using Aprolium. Prevention is assuring clean water supplies and dry feeding grounds. A sulfamethozine can be added to the water for five days each month as a prevention. Aprolium is used for 21 days and may not be repeated. Avoid overcrowding, feeding on wet ground and contaminated water troughs. Monesin or rumensin in the feed can prevent coccidiosis, but they are expensive and dangerous to horses. Large commercial water troughs that cannot be cleaned daily can be chlorinated to control coccidia. Remember that a herd can be infected with coccidia and show no clinical effects aside from “doing poorly”. Also, it is a good idea to routinely treat newly weaned kids with anti-coccidial agents even in herds that have never had a problem with coccidia. Coccidia are normally present in the gut and can multiply with the first sign of stress.