Coccidiosis is a costly, profit-stealing intestinal disease that affects millions of cattle each year, particularly young and stressed animals. Caused by microscopic protozoan parasites — specifically Eimeria bovis and Eimeria zuernii in cattle — this parasite attacks the intestinal lining, leading to poor growth, bloody diarrhea and in severe cases, death.
To protect your herd’s health and your bottom line, here are six facts you need to know about coccidiosis:
1. Dewormers Won’t Work
Many producers mistakenly assume all internal parasites can be wiped out with a standard deworming protocol that targets nematodes. However, coccidia are protozoa that are not affected by standard deworming treatments.
Coccidia species are also highly unique to the animals they infect. According to Dr. A.J. Tarpoff, Kansas State University Extension veterinarian, in a K-State coccidiosis publication, “Coccidia are very host-specific, meaning only cattle-specific species will cause disease in cattle.”
2. Stress Is the Ultimate Trigger for an Outbreak
The parasites are highly opportunistic. They often lie in wait for an animal’s immune system to drop before taking hold and multiplying rapidly.
“Coccidiosis is frequently referred to as an opportunist — a disease that develops when other stress factors are present,” Tarpoff says. “Clinical signs of coccidiosis usually are present at, or shortly following, stress such as weather changes, weaning, overcrowding, long truck rides, unsanitary conditions, large exposure and other disease conditions such as shipping fever.”
3. Beware of the “Silent Shedders”
Just because calves look healthy doesn’t mean pastures or feedlots are coccidia-free. Cattle can shed infectious oocysts in their manure without exhibiting diarrhea, loose stools or lethargy.
“Most cattle carry some level of coccidia, even though they do not show clinical signs,” Tarpoff explains. “They will appear clinically healthy even though many may be shedding oocysts.”
Because animals can shed oocysts silently — or conversely, develop watery diarrhea before oocysts are even detectable in a lab sample — Tarpoff emphasizes diagnosis requires matching herd clinical signs with veterinary evaluation rather than waiting on a single fecal test.
4. Oocysts Act Like Armored Tanks in the Pen
Once infected animals shed oocysts (the egg-like stage of the parasite) in their manure, those organisms act like microscopic armored tanks in your pastures and pens. Due to their durable outer shell, they persist in dry lots, muddy pens and holding facilities far longer than many viral or bacterial pathogens.
“Oocysts are extremely resistant to environmental stress and are difficult to completely remove from the environment,” Tarpoff warns. “Oocysts are frequent contaminants of feed and water and when the sporulated oocysts are ingested by other animals they start the life cycle over in the new host.”
To break the chain of reinfection, Tarpoff recommends never feeding on the ground, keeping pens scraped to reduce manure buildup and cleaning water tanks regularly — daily during an active outbreak.
5. Severe Cases Can Trigger Neurological Symptoms
While watery or bloody diarrhea, dehydration and weight loss are the traditional hallmarks of intestinal damage, severe coccidiosis infections can actually cross over into central nervous system issues.
“‘Nervous coccidiosis’ is a nervous system condition associated with coccidia infection,” Tarpoff says. “Signs are consistent with central nervous system involvement, and include muscle tremors, convulsions and other central nervous symptoms. A consistent sign in ‘nervous cocci’ cattle is that stimulation of any type seems to trigger the symptoms. Death may follow the acute disease either directly or from secondary diseases such as pneumonia.”
6. Stop the Spread with Immediate, Pen-Wide Action
When clinical coccidiosis breaks out in a pen — marked by straining, watery or blood-streaked manure, and dehydration — treating individual animals is only half the battle. Because the protozoan spreads through shared feeding and watering spaces, pen mates are likely already infected.
If an outbreak occurs, Tarpoff recommends a three-step immediate response:
- Separate sick animals from healthy herdmates.
- Treat sick animals with effective medication as prescribed by a veterinarian, addressing dehydration and anorexia alongside the infection.
- Initiate mass or pen-based medication, as pen mates are almost certainly exposed and incubating the parasite.
“In most confinement situations, prevention or control with coccidiostats is a wise strategy,” Tarpoff concludes. “Labeled coccidiostats available for prophylaxis include amprolium, monensin, lasalocid and decoquinate. These products affect different stages of the life cycle of coccidia, thus sound veterinary advice is needed in the choice of products.”
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