– Dr. Michelle Arnold, DVM – Ruminant Extension Veterinarian (UKVDL)
What is “coccidiosis”?
Coccidiosis, also known as “cocci”, is a disease of calves due primarily to two species of protozoan parasite, Eimeria bovis and Eimeria zurnii. In the clinical or observable form of the disease, calves have diarrhea, often bloody, that can lead to death from damage to the intestinal tract, specifically in the lower small intestine, cecum, and colon. “Subclinical” infection without noticeable diarrhea can still cause gut damage resulting in depressed appetite, decreased feed efficiency, and poor weight gain. How “sick” animals get depends on which species of Eimeria is involved, the level of exposure, and any associated stressors such as weaning, transport, poor nutrition or weather extremes occurring at the time of infection. Coccidiosis can be seen in calves as early as 3 weeks of age, but it is diagnosed most frequently at stressful times such as weaning or at entry to a backgrounding operation or feedlot. Cattle generally develop immunity to disease by 1 year of age, meaning they continue to harbor and shed coccidia without the ill effects. Healthy older animals can spread the organism to younger, vulnerable stock.
How is the organism transmitted?
All bovine Eimeria have a “fecal-oral transmission cycle”, in which the infective form of the organism (the “oocyst”) is passed in the feces of infected cattle and consumed by calves in contaminated feed or water. Coccidia are “host-specific”; the Eimeria species that infect cattle do not infect any other species of animal and vice-versa. Calves infected for the first time shed the greatest number of the infective “oocysts” and quickly contaminated their environment. The life cycle of Eimeria is completed in a calf within 2-4 weeks and millions of oocysts may be produced in that time. Once the oocysts leave the calf in the feces, the oocysts “sporulate” and can survive weeks to months outside in the right conditions of moderate temperature and high moisture. Buildup is most common in areas where animals congregate or are crowded together, especially around watering and feeding facilities. However, direct exposure to sunlight and drying will kill the organism.
Figure 1: From “Coccidiosis in Large and Small Ruminants”, Veterinary Clinics of North America, Food Animal Practice (2018), 34, p.202.
What does a calf with coccidiosis look like?
After a calf swallows sporulated oocysts, the organism begins a very complex reproductive cycle, both asexual and sexual, within the cells that line the calf’s intestinal tract (see Figure 1 for a complete review of the life cycle). When the reproductive cycle is finished and the newly formed oocysts are mature, they break open the intestinal cells and are released into the gut and passed in the feces. The damage to the gut caused by this rupture of intestinal cells is what causes the disease symptoms. The most common sign associated with coccidiosis is diarrhea that often contains red blood, mucous and shreds of intestinal lining. Calves often strain and some calves may prolapse the rectum with excessive straining. Milder cases may have watery or soft stools, depressed appetite, rough hair coats and poor growth. The disease can range from self-limiting infection in which calves require no treatment, to severe infection and death. Some animals develop nervous signs including tremors, circling, and convulsions with normal periods between neurologic episodes. Mortality (death) in those with the nervous form is typically 8090%. Calves that recover from severe diarrhea may have permanent scarring in the gut and never grow well. Coccidiosis should always be considered a “herd disease” rather than an individual calf problem because Eimeria spread quickly within a group after just a few life cycles of the parasite.
How is the disease diagnosed?
Observation of diarrhea in stressed calves, especially with red blood present, raises the suspicion of coccidiosis. Fecal samples may be collected and analyzed in the laboratory for Eimeria oocysts, with 500 or more oocysts per gram of feces considered important. However, since the organism reproduces by both sexual and asexual means, severe disease can result before oocysts are detected in large numbers in the feces. Therefore, it is recommended to collect fecal samples from multiple animals in a group when attempting to confirm the diagnosis. Of note, there are at least 13 species of Eimeria in cattle and many are considered “nonpathogenic” and will not cause illness, so species differentiation is required. The rare form of “nervous coccidiosis” is diagnosed most often at necropsy.
Is there a treatment available?
In cattle, once the oocysts are detected in the feces of a calf with bloody diarrhea, most of the intestinal damage is already done. However, treatment can still have a beneficial effect and can slow transmission to the rest of the herd. All calves in a group should be treated simultaneously and moved to a cleaner environment or new pasture once the disease is recognized. Amprolium (Corid®) is licensed in cattle for therapeutic treatment when given for 5 days at 10 mg/kg body weight and can be used for prevention at a dose of 5 mg/kg of body weight for 21 days. Amprolium is a “thiamine analogue” and it is taken up by the coccidia in place of thiamine, thus interrupting several critical metabolic steps in its growth and reproduction. Corid® is available as an oral solution, a pelleted feed additive, or as a soluble powder. It is important to observe the correct dose and length of treatment because too much amprolium can result in polioencephalomalacia or “brainer” calves. Talk with your veterinarian for more information.
Sulfaquinoxaline administered as a 0.015% solution in water, is also approved as a treatment in cattle at 10-20 mg/kg body weight for 3-7 days. Sulfa drugs interfere with the synthesis of folic acid, an essential requirement for reproduction in the life cycle of coccidia.
Can coccidiosis be prevented?
Prevention is far better than treatment since production losses and permanent gut damage in a proportion of calves is nearly guaranteed once diarrhea is observed. Effective coccidiosis control does not require complete elimination of the organism. Instead, consumption of low numbers of oocysts is beneficial because it promotes development of immunity which will protect the animal when challenged with future infections. Minimizing stress and environmental contamination while optimizing nutrition will limit the progression of coccidiosis. However, where environmental control is not adequate (for example, a crowded dry lot) and when times of elevated stress are expected such as at weaning, effective drugs are available to help prevent coccidiosis. Two types of drugs, “coccidiostatic” and “coccidiocidal”, are available. Coccidiostats inhibit the development of early life cycle stages and include amprolium (Corid®), decoquinate (Deccox®), and the sulfonamide antibiotic Sulfaquinoxaline. Coccidiocides kill the parasites at several stages of development and include the polyether ionophores known as monensin (Rumensin®) and lasalocid (Bovatec®), and the symmetric triazine class of drugs which are currently unapproved in the USA.
The most commonly used drugs to control coccidiosis are the ionophores, specifically lasalocid (Bovatec®) and monensin (Rumensin®), and the quinolone coccidiostat decoquinate (Deccox®). They are highly effective, easily administered in feed or minerals, and should be offered for at least 28 days. Lasalocid (Bovatec®) is approved for control of coccidiosis in cattle up to 800 pounds when fed at 0.45 mg/pound of body weight/head per day up to a maximum of 360 mg per head per day. Monensin (Rumensin®) is approved for prevention and control of coccidiosis in many classes of cattle, either mixed in feed at 0.14-0.42 mg monensin/pound of body weight/head per day up to a maximum of 200 mg per day or offered in free-choice products at 50-200 mg monensin per head per day. Decoquinate (Deccox®) is approved to be administered at 0.5 mg/kg of body weight per head daily for at least 28 days for prevention of coccidiosis during periods of exposure to coccidia or when cattle are considered at high risk. As mentioned previously, amprolium (Corid®) can be used for prevention at a dose of 5 mg/kg of body weight/head daily for 21 days.
As always, your veterinarian is the best resource for diagnosis of all medical conditions, treatment, and prevention recommendations.