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CONTRIBUTOR(S): Mike Taylor, Paul Wood,



Coccidiosis is a disease caused by tiny protozoan parasites (mainly of the genus Eimeria), which develop and reproduce within the lining cells of the gut of a range of different hosts.

Calf diarrhea due to coccidiosis
©Peter Jackson


All animals have their own coccidia species and will harbour coccidia without showing disease. Clinical disease may be seen in times of starvation, debilitation or other stresses which affect the immune system. In livestock, disease due to coccidia is essentially a consequence of intensification.

With a few exceptions, coccidia are also host-specific so that each coccidia species only infects one host species. This means that cattle coccidia only infect cattle; sheep coccidia only infect sheep and so on. Consequently, a common myth that poultry manure spread onto land may cause coccidia infection in grazing cattle or sheep is completely unfounded.

How is coccidiosis spread?

Coccidiosis is spread through the ingestion of infective stages of the parasite. Coccidia have a life cycle in which the different stages develop within the host’s intestinal cells by asexual and sexual reproduction eventually producing a protective cyst stage, called an oocyst. Oocysts, like worm eggs, are passed out in the feces and need to undergo further development before they become infective to the next host. Infected calves produce billions of oocysts that contaminate the environment in which they live. Under intensive production, systems become heavily contaminated and are a constant source of infection to other calves.

Cattle are host to a number of different coccidia species, but not all species are pathogenic and cause disease. There are, however, some species that are very pathogenic and which are capable of causing significant levels of infection, leading to clinical disease and even death in calves.

During the first few months of life, the majority of calves will probably have been infected with coccidia. They may or may not, show signs of disease depending on a number of factors and in particular the levels of infection they encounter. Disease is most commonly seen in young calves.

What are the effects of coccidiosis?

Losses caused by subclinical coccidiosis can be high and result from marked decreases in growth rate, liveweight gain and poor food utilization. Estimates on the losses due to the effects of subclinical coccidiosis in dairy cattle in the UK vary between £24 and £59/animal.

Clinical signs of coccidiosis are usually diarrhea and failure to thrive. Affected calves eventually lose their appetite and become weak and unthrifty. In acute coccidiosis, infected calves show profuse watery diarrhea, often containing streaks of blood. If left untreated, these animals may continue to scour and eventually die of dehydration.

Cattle that reach adulthood are highly resistant as they develop a strong immunity but will continue to harbor small numbers of coccidia throughout their lives. Occasionally acute coccidiosis occurs in adult cattle with impaired immunity or in those which have been subjected to stress.

How do I confirm the presence of coccidiosis?

Coccidiosis should be suspected if there is scouring with blood in the feces. The diagnosis of coccidia in not always straightforward and your veterinarian may confirm the diagnosis either by post mortem of dead calves or by submitting feces taken from scouring calves to the laboratory. In the laboratory, simply finding or counting coccidia present in feces is not sufficient, and the species present should also be examined for the presence of known pathogenic species. Species identification is a specialist skill. Your veterinarian may be trained in this technique, or may send samples to a specialist laboratory.

What risk factors influence disease occurring?

Colostrum generally provides calves with passive immunity, during their first few weeks of life.  Colostrum intake can vary depending on the levels and standards of husbandry. Ensuring new-born calves suckle, and get colostrum soon after birth, is extremely important in protecting against coccidiosis, and indeed many other diseases.

Resistance to coccidia, within the animal, can be reduced by adverse conditions that affect the immune system such as changes in environment or diet, prolonged travel, extremes of temperature and weather conditions, or severe concurrent infections with other viral, bacterial and parasitic diseases.

Calves kept indoors on damp, contaminated bedding are particularly at risk. As are those reared on contaminated heavily stocked permanent pasture, especially during cold wet weather.

What steps should I take to prevent coccidiosis?

Simple measures that you can take to help reduce disease risk include:

  • Providing dry bedding.
  • Avoidance of overcrowding.
  • Minimizing stress.
  • Reducing stocking densities.
  • Batch rearing of calves and avoidance of mixing different age groups.
  • Provide plenty of clean bedding in calving and rearing pens.
  • Keep young calves off heavily contaminated permanent pastures.
  • Good feeding of the dams prior to calving and creep feeding will also help to boost immunity.
  • Hygiene plays a major part in the control of coccidiosis.
  • Regularly moving food and water troughs, and raising or covering them to prevent fecal contamination, can help reduce the levels of infection.
  • It is good practice to clean and disinfect all buildings between groups of calves.
  • Provide clean pasture for calves turned out to grass.
  • Steam cleaning or pressure washing helps remove faecal debris and it is important to use a disinfectant that claims activity against coccidia oocysts, as not all disinfectants will kill them. Those that are effective are either ammonia-based or contain chlorophenol (chloro-m-cresole).

What treatments are available?

There are several anticoccidial treatments available for use in cattle which can be given to prevent and control coccidiosis outbreaks. Your veterinarian will be able to advise you as to the best treatments for your stock. Commony used treatments include decoquinate given as part of a creep feed for 28 days. Alternatively products containing diclazuril or toltrazuril can be given as a single oral drench prior to anticipated disease risks.

The timing of these treatments is critical. Disease in calves often occurs from 3-4 weeks of age and follows one of the stress factors identified above. Under these circumstances the treatment should be given about two weeks after the identified stress factor. The reasoning behind this is that the parasites life cycles takes about 18-21 days to complete; treating around 14 days breaks the parasite life cycles at a point where sufficient damaging numbers have not developed, but the parasite exposure allows immunity to develop.

In situations where contamination levels vary, subsequent or delayed treatments may be required.

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