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Don’t assume it’s coccidiosis: Tips for recognizing symptoms and diagnosing accurately

Jerry Mechor for Progressive Dairy Published on 07 May 2021

The majority of dairy producers are familiar with coccidiosis – a disease that has the potential to inflict significant economic losses on a dairy operation.

Even though research has told us a lot about how to prevent and control this protozoan disease, without proper diagnostic testing and investigation it’s difficult to accurately diagnose coccidiosis. A thorough investigation that includes examining animal history, environment, feed management and the cocci control products being used must be part of a comprehensive diagnostic plan.



Coccidiosis causes significant global losses in cattle and bison, estimated at $400 million to $700 million annually. These losses include animal mortality, growth reduction, permanent stunting, feed conversion reduction, treatment expenses and prevention costs. Coccidiosis may also cause a reduction in daily weight gain, increased susceptibility to other diseases and poor response to therapy for other conditions.

Combining investigative information from farms experiencing cocci outbreaks with an extensive literature review on the subject has given us new insights about the importance of a thorough investigation of suspected cases on the dairy to ensure an accurate diagnosis is made. An accurate coccidiosis diagnosis is critical to developing a cost-effective treatment plan, but having a solid prevention strategy in place can mitigate the risk of disease in the first place.

Here are some tips for coccidiosis diagnosis and prevention.

Obtain an accurate diagnosis

Coccidiosis is caused by a pathogenic species from the genus Eimeria. In cattle, 13 intestinal Eimeria species have been identified, although not all cause disease in animals. Eimeria bovis and Eimeria zuernii are two species that have been shown to have the greatest potential for disease infection. This is important because although lab results may indicate a high number of coccidiosis oocysts in an animal’s feces, species identification is critical to confirming the presence of species with pathogenic potential.

Oocysts will transiently be shed throughout an animal’s life. Many cows will experience a transient increase in fecal shedding in the periparturient period, and calves will shed more oocysts than older animals. Calves can shed hundreds to a few thousand or more of oocysts per gram (opg) of feces. In clinical cases, shedding rates of over 5,000 to 10,000 opg of pathogenic species are typically considered significant. This is why it is important to understand the quantitative counts and speciation to accurately diagnose.


While diarrhea is one of the most common symptoms of coccidiosis, producers should look deeper for an accurate diagnosis. Diarrhea in calves has many causes and does not always equate to coccidia. Producers should take a comprehensive approach to the diagnostics to gain insight into what’s occurring. Bacteria, viruses, parasitic infections, dietary changes and nutrient deficiencies are other common causes of diarrhea in weaned calves.

Achieving an accurate diagnosis of coccidiosis requires several steps:

1. Look for clinical symptoms and conduct a thorough examination of sick calves.

2. Conduct necropsy examinations on dead animals.

3. Confirm the presence of pathogenic species of Eimeria oocysts through lab testing.

Lab testing is vital for confirming coccidiosis in cattle. We recommend obtaining five to eight samples of feces from calves that are both healthy and suffering from disease. Submit them for virology, bacteriology and parasitology testing, and be sure to look at cocci speciation on the lab report.


Once lab results are in, a positive diagnosis of coccidiosis can be made by:

  • Confirming a significant number of pathogenic coccidian species in feces (less than 5,000 to 10,000 opg)

  • Assessing appropriate clinical symptoms, including diarrhea and dysentery

  • Confirming by pathology, if appropriate

  • Ruling out other diseases

Based on the diagnosis, producers can institute a treatment and prevention plan, whether it is for coccidiosis, challenges with bacterial overgrowth due to diet changes or other intestinal issues.

Take action to keep calves healthy

Eimeria oocysts can remain viable in the environment for up to a year, withstanding environmental challenges because they have a thick cell wall that helps protect them. They’re resistant to freezing, extreme pH changes and low oxygen availability, meaning they can thrive in extreme conditions. One key to prevention is a clean environment for animals with plenty of exposure to direct sunlight, which can be detrimental to oocyst survival. Covered areas that are wet and contaminated with feces provide a favorable environment for disease transmission.

Another way to help prevent the spread of disease is to reduce animal stress, since stressed cattle may be more prone to coccidiosis infection. Weaning, transporting, extreme weather, changing diets and overcrowding are all factors that could place animals at greater risk of developing coccidiosis.

Environmental management to minimize exposure of animals to fecal-contaminated housing, feed, water and soil is critical to preventing coccidiosis. I recommend taking these actions to keep cattle healthy:

  1. Ensure cows are clean before entering maternity areas.
  2. Minimize the time newborn calves spend in the maternity pen.

  3. Clean maternity pens regularly.

  4. Thoroughly clean calf housing to remove all organic matter; expose to direct sunlight if possible.

  5. Minimize contact between milk-fed calves.

  6. Isolate animals with severe clinical symptoms.

  7. Avoid feeding on the ground.

  8. Maintain clean waterers and feeders.

  9. Avoid overcrowding and reduce stress.

  10. Rotate pastures.

  11. Encourage early dry matter intake (DMI) in young calves.

  12. Provide adequate levels of a feed additive containing an ionophore.

For the prevention and control of coccidiosis, using an ionophore is key. Ionophores are cidal in nature and will kill coccidia at multiple stages of the life cycle instead of merely arresting their development. The combination of reducing infective oocysts in the environment through sanitation and using an effective ionophore can minimize emergence of clinical cases of coccidiosis.

Taking appropriate steps to prevent coccidiosis and accurately diagnosing positive cases can help dairy producers save time and money. Treating for the disease without confirming it’s the cause of symptoms in cattle is a costly mistake. We’ve often looked at this disease with tunnel vision. The traditional thought has been, “If we have diarrhea, we have coccidiosis.” The reality is: It’s not that simple.

Consult with your veterinarian regarding the health of your dairy calves and to determine if coccidiosis is a problem in your herd.  end mark

PHOTO: An accurate coccidiosis diagnosis is critical to developing a cost-effective treatment plan, but having a solid prevention strategy in place can mitigate the risk of disease in the first place. Photo provided by Elanco Animal Health.

References omitted but are available upon request. Click here to email an editor.

Jerry Mechor
  • Jerry Mechor

  • Technical Consultant
  • Elanco Animal Health
  • Email Jerry Mechor