Coccidiosis in cattle is caused by the protozoan parasites Eimeria bovis, Eimeria zuernii, and Eimeria auburnensis. Coccidia are intracellular parasites of many organs and tissues in cattle.

Coccidial infections in cattle are typically not clinically apparent. Subclinical infections will damage the absorptive surface of the intestines and will weaken the immune system. The interference with nutrient absorption in turn causes poorer feed efficiency, slower weight gain, or even weight loss. The end result of this interference is monetary loss. Since the immune system is weakened, it will increase the animal’s susceptibility to other bacterial and viral infections.

Clinical signs of disease occur more frequently when animals are housed or confined in small areas or when especially young cattle are stressed by extremes in the weather. Clinical signs may include dysentery, matting of fecal material around the tailhead, tenesmus (straining during defecation), diarrhea sometimes with blood, rough and dull hair coat, and central nervous signs.

Central nervous signs are rare but consist of muscle tremors, hyperaesthesia ( increases sensitivity of nerves in the skin), convulsions, nystagmus (rotating of the eyes back and forth), and high mortality rates of up to 50%. Almost all cases of nervous coccidiosis occur in the coldest portions of the year, January to March. The pathogenesis of nervous coccidiosis is presently unknown. Secondary complications such as pneumonia may occur in severe cases of cocciodosis. Mortality with coccidiosis is low unless accompanied by central nervous system signs or secondary infections.

Oocysts or eggs are passed in the stool from infected individuals. The oocysts may remain infective for up to a year in soil, upon porous wooden surfaces, and on the hair coats of animals. These oocysts then undergo a process called sporulation, which allows them to become infective. The length of time before which oocysts become infective will vary according to the species involved and the environmental conditions that are present. Moist conditions aid sporulation whereas dry conditions tend to impede it. Sporozoites released from ingested oocysts invade the intestinal epithelium. These sporozoites take over the intestinal cells multiplying within and eventually causing rupture of the invaded cells. Their replication results in the destruction and exfoliation of the mucosa, causing diarrhea and hemorrhage. Mature oocysts are eliminated by the cow in their fecal material. The entire life cycle of this parasite takes from 21 to 28 days.

Coccidia are easily diagnosed through a stool sample taken by a veterinarian. A differential diagnosis should include bacterial infections such as salmonella, Bovine Virus Diarrhea (BVD), and other intestinal parasites which may occur alone or simultaneously with coccidia.

There are three types of medication used for the treatment of coccidiosis in cattle: Coccidiocide, Coccidiostats, and Ionophores are all available. A coccidiocide is a folic acid antagonist. A coccidiocide results in the death of coccidia as they emerge from the invaded cells of the intestinal lining and thereby preventing them from invading new cells. Sulfonamides in the feed at 25-35 mg/Kg for 15 days or more are an effective Coccidiocide.

A coccidiostat suppresses the full development of the entire coccidial life cycle and thereby allows time for the cattle to develop natural immunity to the infection. Amprolium (trade name Corid®) is a drug manufactured by Merial. Corid® resembles thiamine (Vitamin B1), which is required in large amounts by the rapidly multiplying coccidia. Coccidia starve when they ingest Corid®, thereby arresting development.

Monensin® is an Ionophore which is usually sold as a feed additive to promote growth and feed conversion in cattle. The dose must be carefully monitored to prevent toxicity and under no circumstances should horses be fed feed contaminated with Monensin since they are ten times more susceptible to toxicity from this particular drug. Lactating dairy animals should also not be fed Monensin.

Decoquinate (trade name Deccox®) is often recommended as an aid in the prevention of coccidiosis caused by Eimeria species. It is fed during periods of high risk of exposure to oocysts, but it is ineffective in the treatment of established infection.

To control coccidia, avoid crowded and damp housing conditions. Clean calf hutches with a power sprayer between calves and locate these hutches far enough apart to prevent contact. Raise feed and water troughs off the ground and avoid feeding hay on the ground. Pastures should always be rotated for parasite control.


References:
Georgi, Jay, and Marion. Parasitology for Veterinarians. Fifth Edition. W.B. Saunders. 1990. pp 88-89.
Aiello, Susan. Editor. The Merck Veterinary Manual. Eighth Edition. 1998. pp1890