Cryptosporidiosis in Calves

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Cryptosporidiosis in Calves

Also known as



Cryptosporidiosis is a protozoal disease. Protozoa are one-celled animals. Most kinds are harmless but several types cause disease and most of these are transmitted by the fecal-oral route; the protozoa are passed in feces of an infected animal and ingested by a susceptible animal via contaminated feed or water or when licking a dirty hair coat or suckling a dirty udder.

The protozoa that cause cryptosporidiosis are found almost everywhere. Various types infect humans, sheep, goats, deer, squirrels, and other animals but Cryptosporidium parvum is the one that infects cattle. This same type can also infect humans. Another strain affects only humans. There are 19 species and 40 genotypes of Cryptosporidium.

Several strains affect humans and other animals but not cattle. Wildlife occasionally pass crypto to livestock. These protozoa survive in moist conditions and can live for about 170 days in streams of water or on wet, contaminated pastures, but drying or freezing will eventually kill them.

The protozoa that cause cryptosporidiosis are cousins of coccidia. Observed under a microscope, they look like a tiny coccidia and are a lot harder to see. A special stain must be used in order to see Cryptosporidium protozoa.

In earlier years, this disease was just a problem in dairy calves and estimated to affect up to 70% of dairy calves 1 to 3 weeks of age, with rate of infection on some farms as high as 100%. Now this disease appears in beef herds as well. Though crypto is often mild and self-limiting (runs its course without treatment and the animal recovers), it can be life threatening in any human or young animal with a compromised immune system or concurrent illness with another disease. Concurrent infections with other intestinal pathogens, especially rotavirus and coronavirus, are common. Diarrhea is more severe in mixed infections.

The life cycle of Cryptosporidium consists of six major developmental stages. After ingestion of the oocyst, it releases infective sporozoites that go through asexual multiplication to form gametes. This stage is followed by fertilization, oocyst wall formation, and sporozoite formation. The oocysts can sporulate within the tissue cells of the host animal and are infective when passed in feces. Infection persists until the host’s immune response eliminates the parasite.

In most cases, the diarrhea is self-limiting after several days. Only rarely do severe dehydration, weakness, and collapse occur, in contrast to other causes of acute diarrhea in young calves. Fatality rates can be high, however, in herds with cryptosporidiosis when the calf feeder withholds milk and feeds only electrolyte solutions during the episode of diarrhea. The persistent diarrhea leads to huge energy deficit in these circumstances, and these calves may die of starvation at 3 to 4 weeks old.

Crypto is a disease of young calves, especially 1 to 3 weeks of age, and not something you’ll see in calves that are 3 or 4 months old. This is different than coccidiosis which takes several weeks’ incubation (you won’t see coccidiosis until the calf is at least 4 weeks old), and which can affect older calves, even at weaning age.


  • Dullness
  • Lack of appetite
  • Dehydration
  • Mild to moderate diarrhea
  • Feces yellow or pale, watery, and contain mucus
  • Weight loss
  • Emaciation

Note - With cryptosporidiosis in calves, signs include diarrhea that persists for several days, age at onset is later and the duration of diarrhea longer than in diarrheas caused by rotavirus, coronavirus, or Escherichia coli.


The source of cryptosporidial infection is oocysts that are fully sporulated and infective when excreted in feces. Large numbers are excreted by a sick calf, resulting in massive environmental contamination.

Transmission may occur directly from calf to calf, or indirectly via fomite or human transmission, from contamination in the environment, or by fecal contamination of the feed or water supply. C. parvum is not host-specific, and infection from other species such as rodents or farm cats via contamination of feed is also possible.

After being ingested, the protozoa multiply in the calf’s intestine, causing diarrhea. It’s rare to find this pathogen in calves older than 4 months or in adult cattle, but many beef and dairy calves are infected during their first weeks of life.  

In one study, 5% of cows tested were carriers, spreading a few protozoa in their feces. Most cows shed other species of crypto (that are relatively harmless) but a few cows shed parvum oocysts. Thus the calf may pick it up from the dam’s feces in the first days of life.

Generally calves are the main source of infection for other calves; if they become infected they serve as incubators for the protozoa and shed greater numbers than the cows do, contaminating pens and pastures.

These organisms are common in the environment and the water on certain farms. This disease can be deadly if young calves are challenged with several pathogens at once, such as bacterial and/or viral scours along with the protozoa. Calves with severe, hard-to-treat diarrhea usually have mixed infections.

It’s important to keep calving cows out of contaminated pastures and have them calve on clean pastures, so their calves won’t immediately pick up oocysts. Cows may be the original source, but the calves multiply it and serve as incubators for the protozoa, exploding the parasite population.
In any herd there are probably several calves that pick up a few oocysts that might be seen in a fecal sample, but whether calves get sick may depend on how much they are exposed to. It’s not uncommon for calves to have a few oocysts; it’s when they get loaded up that problems occur.

The more you can do to improve the vigor and health of calves (with good nutrition and minimal stress) and try to decrease the amount of crypto in the environment, the more likely you’ll avoid diarrhea. Stress is often a factor; calves may break with crypto during bad weather.


Crypto is hard to prevent or treat because it’s not viral or bacterial and it’s difficult to create an effective vaccine against protozoa. There are almost no vaccines for protozoal diseases. 

The interesting thing about immunity in calves and humans, however, is that once they’ve gone through the natural infection they don’t seem to get it again. They build immunity, but scientists  have not been able to replicate that with a vaccine.

Prevention therefore depends on good management. In a dairy, it’s all about nutrition, hygiene and trying to minimize fecal-oral contact. The best defense against crypto is a healthy herd in good condition, in a clean environment.

Herd health can be compromised by improper nutrition, so if you are dealing with crypto you need to look at trace mineral status of the animals—especially selenium and copper, since those are crucial to a strong immune system.

In beef calves we tend to see problems when there’s overcrowding in a calving pasture, especially in wet, bad weather. The protozoa are resistant to most disinfectants, so anything a person can do to keep the later-calving cows moved to clean pastures will help, and avoid overcrowding.

The later-born calves in contaminated pastures are the ones that usually get sick. The protozoa don’t live in the environment forever, but can live for several weeks or months.

Many cases are weather related or due to inadequate nutrition, inadequate shelter or bedding.  Animal husbandry practices can make a big difference in prevention.

Try not to bring this disease to your place if you don’t have it already. Since it’s a common problem in dairy calves, don’t buy dairy calves to raise on bottles or nurse cows, or to graft on beef cows that lost their own calves—unless you are sure the dairy calves are healthy and have never been exposed to crypto.

Even if they look healthy, isolate them for 5 days after you bring them home, to be sure they are not incubating the disease. Then if they develop diarrhea you can clean up the isolation pen and haven’t exposed other calves. Don’t buy cows from any herd or farm known to have crypto.

Calves should be born in a clean environment, and adequate amounts of colostrum fed at an early age. Calves should be kept separate without calf-to-calf contact for at least the first 2 weeks of life, with strict hygiene at feeding. Any calves with diarrhea should be isolated from healthy calves, and for several days after recovery.

Care must be taken to avoid mechanical transmission of infection. Calf-rearing houses should be vacated and cleaned out regularly--with thorough cleaning and several weeks of drying between batches of calves. Rats, mice, and flies should be controlled when possible, and rodents and pets should not have access to calf grain and feed storage areas.

When we get crypto in calves, we need to identify the underlying cause and why those calves were at risk. Is there BVD in the herd?  Or is it due to gestational nutrition such as inadequate protein in the cows’ diets?  Did the calf fail to get colostrum, or adequate colostrum?


Treatment is challenging. Unlike bacteria, we can’t kill protozoa with antibiotics. We don’t have any drugs that have been shown to work as an effective treatment.
If calves get diarrhea, the main focus is to keep them hydrated, using a good quality oral electrolyte solution and good supportive care. Hopefully, within 5 to 6 days the scours will stop.

If the calf gets weak or unable to stand, he needs IV fluids. If the calf is still walking—just dumpy and scouring—you can probably just use oral electrolytes.

If it’s a beef calf, bring the cow and calf in from the pasture for treatment, to have access to the calf for daily care. Then you don’t have to chase him around to catch him, and stress him. Sometimes he’ll look better after a couple days of electrolytes and you think he’s ok and then 2 days later he’s gone downhill again.

If you keep him and his mother in where you can give him electrolytes every day, you make better progress.

Crypto causes a secretory diarrhea (electrolytes secreted into the intestine).These calves are losing fluid and lots of bicarbonate and become very acidotic. In order to save them you must use a good electrolyte solution that’s high in bicarb content, and lots of it; give 2 quarts, 3 to 4 times a day. The more often, the better.

Antibiotics are usually given, even though they are ineffective against the protozoa; a broad-spectrum antibiotic may be needed to combat secondary infections and enable the gut to heal. Instead of pills, many veterinarians think it works better to give an injectable antibiotic and an oral probiotic paste to help get the good bugs re-established in the gut.
Viral scours (rotavirus and corona) and crypto cause enough gut damage that the calf may still have abnormal feces even after the disease has run its course. It takes several days for the gut to heal enough to absorb fluid and nutrients and function normally.

The calf won’t immediately have a normal stool; sometimes it will be pasty, but you don’t need to keep giving antibiotic. If the calf is eating again, let the immune system heal the body. Just keep up the fluids as long as the calf has any diarrhea.

Stockmen often use medications like Keopectate or Pepto Bismol to help soothe the irritated gut lining and slow the gut contents. These may help a little, but the main thing is to keep up the fluids so the calf won’t dehydrate. If you are only giving fluid and electrolytes once a day, it’s not nearly enough. 

Very young calves with serious diarrhea will dehydrate quickly and you may need to give fluids at least 3 or 4 times a day and sometimes even more often, to keep ahead of it—or put them on an IV.

If it’s a beef calf and still nursing the dam, this will help the calf nutritionally. For a dairy calf, cows’ whole milk should be given in small quantities several times daily (to the full level of requirement) to optimize digestion and minimize weight loss. Several days of intensive care and feeding may be required before recovery is apparent.    

When treating sick calves, remember that Cryptosporidiosis can be spread from calves to humans. Calves or humans in good health can usually be exposed and not become ill. Very young calves or humans, or elderly people, or anyone with a compromised immune system (with HIV, or taking immune-suppressant drugs) may become seriously ill.

Crypto can cause devastating illness in vulnerable people or calves, such as calves that did not receive colostrum at birth. Be careful when treating sick calves (and wear exam gloves) so you don’t inadvertently spread disease to a vulnerable human.

Wash hands and change clothes when you come indoors, especially if there are young children or elderly adults in your home. There is human risk with this disease—even more than with an E. coli or Salmonella.

Hydrogen peroxide is one disinfectant that will kill crypto oocysts.  If you are working around calves with diarrhea, make sure you protect yourself (and others) from becoming infected.

About the Author

EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.