Understanding when coccidiosis is the cause of calf scours

Russ Daly
When a scours outbreak sweeps through the herd leaving dead calves in its wake, we’d like to know the causative germ. But for most sporadic scours cases, knowing the specific germ is of less importance.

The “germ theory” of infectious disease is well-ingrained in us veterinarians through the multitude of microbiology courses we endure through our education.

By extension, that understanding that animal diseases usually have a specific virus, bacteria or protozoa as their cause filters down to our producer clients. So when we’re faced with scouring calves, the first question asked is, which germ is causing the problem? Is it rotavirus? Coronavirus? Cryptosporidia?

I discuss this question with students in the South Dakota State University course I teach on animal diseases. One of my suggested answers to this question catches some of them off guard: It might not matter.

Really? Don’t we have to know? Not always.

Certainly, when a scours outbreak sweeps through the herd leaving dead calves in its wake, we’d like to know the causative germ. But for most sporadic scours cases, knowing the specific germ is of less importance.

Prompt treatment with oral or intravenous fluids is important for scouring calves, no matter what germ is involved. To be sure, most dairy and beef producers don’t wait around for a diagnosis before treating their scouring calves. Furthermore, the source of calves’ exposure to any of these germs is the same: contaminated environments, often accompanied by cool wet weather. Basic rehydration and exposure prevention doesn’t change based on the germ.

In some cases, however, knowing the germ culprit is necessary to guide a specific, critical treatment choice. Coccidiosis is a prime example.

Coccidiosis is caused by a protozoa spread between cattle through the manure. Like other protozoa, coccidia have complex life cycles consisting of several different stages. The form emitted in a calf’s manure is an “oocyst”: think of it as a very tough, hardy, microscopic egg. The oocyst can survive weeks or months in cattle lots under the right conditions.

Once it’s taken in by the calf, the oocyst hatches, releasing the “baby” coccidia to invade cells in the intestinal lining. They develop into the next protozoal stage, which then infect other gut cells. This process repeats until a new oocyst is formed, released from the gut cell into the manure for the cycle to continue.

The byproduct of all this reproduction is widespread damage to the gut cells. Often, the damage is so profound that it extends to the underlying blood vessels. Diarrhea results when the damaged cells can’t absorb fluid. Blood in the stool results from the blood vessel damage. As a result, calves with coccidiosis typically exhibit a bloody diarrhea.

The other feature of all that protozoal reproduction is that it takes time. It’s only after all those life cycles that the gut damage becomes severe enough to produce clinical signs. For coccidia infections, the shortest time period between exposure and the clinical signs is roughly four weeks. Bloody diarrhea in a calf at least four weeks old makes coccidiosis distinguishable from other scours causes (fecal testing at a vet clinic can be used, too).

Fortunately, in contrast to some scours germs, we have specific treatments against coccidiosis. Amprolium and sulfas can be given to individuals, while decoquinate and ionophores can be fed to groups as preventives or treatments. This is why we want to know whether coccidiosis is causing a scours problem.

Coccidiosis has been around forever, but interestingly, it’s an increasingly frequent topic of calls I get from veterinarians and beef cattle producers. I don’t think the organism is getting any more prevalent or virulent. The widespread use of vaccines and antibody products against other causes of scours might be shifting herds away from those problems, leaving coccidiosis – with no such preventive tools available – as a more prominent cause of problems.

For cow-calf producers, the four-week age is a good time to watch calves for signs of bloody scours due to coccidiosis. Treatment is challenging to manage once calves are out on pasture, but early intervention is frequently successful. Addressing the cleanliness of calving areas is key to preventing future problems.

As always, contacting your veterinarian about treatment and prevention advice is a great first step in managing coccidiosis and all the other health problems that may crop up in your calves.

Russ Daly

Russ Daly, DVM, is the Extension Veterinarian at South Dakota State University