Coccidiosis is a common parasitic protozoan disease of cattle, particularly of weaned calves. Bovine coccidiosis is seen most
frequently in calves that are three weeks to six months of age. Calves become infected when placed on pastures or lots
contaminated by older cattle or other infected calves. Mature cattle may become infected when they are brought in from
pastures and crowded into feedlots or barns.
At least nine species of coccidia occur in cattle, but only two, Eimeria zuernii and Eimeria bovis, cause severe clinical disease.
To a lesser extent, Eimeria alabamensis also can cause clinical disease. The prevalence of the different species of coccidia can
vary considerably between farms, regions, seasons and age groups.
Bovine coccidia have in their life cycle stages both within the host animal as well as outside. The developmental stages in
the animal give rise to a microscopic egg (called an oocyst), which is passed out in the manure.
Under proper conditions of temperature, moisture and oxygen, the oocyst develops within three to seven days and is now
capable of infecting cattle.
Coccidiosis occurs mainly in calves that are three weeks to six months of age and is usually accompanied by diarrhea varying
in severity from watery manure to one containing blood. Animals affected with coccidiosis often strain due to irritation
of the lower bowel and rectum. Blood may appear in the manure after the second or third day of diarrhea. Dehydration,
weight loss, depression, loss of appetite and occasionally death may also be observed.
Infections that fail to produce signs of disease may nevertheless affect the growth and health of an animal by impairing intestinal
function and feed conversion. Calves with only a light infection usually show no signs of disease, but shed oocysts
in manure, so the oocysts accumulate in pastures, yards, barns or on the hair coats so that severe coccidiosis may develop
when new calves are placed in these areas.