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Rotavirus and coronavirosis of the calf
Rotaviruses and coronaviruses are two viruses responsible for a large part of calf diarrhea in the first fortnight of life. They destroy the surface of the small intestine, the one that absorbs water and digests milk. Poorly digested milk r...
What is it?
Rotaviruses and coronaviruses are two viruses responsible for a large part of calf diarrhea in the first fortnight of life.
They destroy the surface of the small intestine, the one that absorbs water and digests milk. Poorly digested milk remains in the intestine, attracts water and causes profuse diarrhea.
The two viruses are very widespread: they circulate in almost all farms without adults being sick. The disease only appears in calves when infection pressure is high or colostrum is lacking.
Key point
A calf that has diarrhea but “looks good” is already losing water with each bowel movement. Now's the time to call, not when he's in bed.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
Watery to pasty diarrhea, often pale yellow, usually appearing in the first or second week of life.
The calf suckles less, then refuses.
Dehydration which sets in within a few hours: sunken eyes, persistent folds of skin, cold mouth.
Dejection, calf which remains lying aside.
Fever is most often absent or discreet.
With the coronavirus, we can also observe stools containing mucus, sometimes tinged with blood, and nasal discharge.
Without complications, diarrhea lasts a few days; fatigue and stunted growth persist longer.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Bovine rotavirus and bovine coronavirus, alone or in combination.
These viruses destroy the cells lining the small intestine. The intestine loses its absorption capacity and its enzyme digesting milk sugar: the milk ferments, attracts water and diarrhea sets in.
Superinfection by environmental bacteria, very common in a damaged intestine, worsens the picture.
Calves poorly equipped with colostral antibodies develop more severe and longer forms.
Late or insufficient colostrum.
Grouped calvings, numerous calves in the same room, mix of ages.
Damp litter, box reused without cleaning.
Cold and wet season, which favors the survival of viruses and weakens the calf.
Primiparous cows, whose colostrum contains fewer antibodies against these viruses.
Passing the same material from a sick calf to a healthy calf.
Transmission
The viruses come out in very large quantities in the stools of sick calves.
Adult cows, especially around calving, can excrete without being sick and contaminate their calves from birth.
Contamination occurs through the mouth: soiled litter, dirty udder, buckets and teats, hands and boots.
These viruses resist well in the external environment, especially in cool and humid conditions, and persist from one calving to the next in poorly cleaned premises.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian prioritizes dehydration and general condition: this is what determines the emergency.
A rapid stool test, carried out on site or in the laboratory, identifies rotaviruses and coronaviruses, often at the same time as coli and cryptosporidia.
This identification is decisive for breeding: it avoids unnecessary antibiotics and makes it possible to choose the vaccine suitable for mothers for the following season.
The age of the calf at the time of the first signs already guides the diagnosis.
Treatment
There is no medicine that destroys these viruses. Treatment involves keeping the calf alive while its intestine repairs itself.
Early rehydration is the essential action, according to the procedures indicated by the veterinarian.
Antibiotics do not act on viruses; they are only justified if the veterinarian suspects a bacterial complication.
The milk diet is maintained, adapted if necessary, because the calf needs energy to rebuild itself.
A calf that can no longer stand requires veterinary perfusion.
Isolation, dry litter, protection against the cold complete the care.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Ensure early, abundant and good quality colostrum intake: this is the only source of antibodies the calf has against these viruses.
Calving in a clean, dry area, clean the udder before the first feeding.
Clean, disinfect and let the boxes dry between two calves; do not mix ages.
Stagger calvings when possible to avoid accumulation of young calves.
Wash feeding equipment after each use.
Treat the sick last, with gloves, and isolate them from the first liquid stools.
Avoid the introduction of animals of unknown origin during the calving period.
Vaccination
Vaccines exist against rotaviruses and coronaviruses, often associated with a valence against certain strains of Escherichia coli.
They are administered to the pregnant cow, at the end of gestation: they enrich the colostrum with antibodies that the calf receives while suckling.
Protection therefore depends entirely on the effective intake of colostrum, early and in sufficient quantity. This is where most vaccination programs fail.
On farms where the disease returns every year, the veterinarian may also advise saving colostrum from vaccinated cows to distribute to the calves during the first days.
The veterinarian sets the timing of the injections based on the expected calving date.
Possible complications
Bacterial superinfection of the damaged intestine, which prolongs and worsens diarrhea.
Severe dehydration and acidification of the blood.
Persistent failure to thrive after recovery.
Increased susceptibility to respiratory illnesses in the following weeks.
Contamination of the premises maintained by sick calves, with serial cases.
When to see a veterinarian
Your calf less than two weeks old has liquid stools: call the same day.
He sucks less well or refuses the bucket.
His eyes sink, the skin on his neck remains wrinkled: dehydration has set in.
He no longer gets up or his body is cold: it's an emergency.
Blood or mucus appears in the stool.
Several calves are affected in a few days: have the agent(s) identified to guide vaccination of the mothers.
Prognosis
A calf rehydrated early usually heals within a few days, with the intestine gradually rebuilding itself.
The prognosis deteriorates rapidly in calves that no longer get up, and when several agents are combined.
Calves with a severe form often remain stunted in growth.
Frequently asked questions
Is an antibiotic useful for viral diarrhea?
No, antibiotics have no effect on viruses. They are only justified if the veterinarian suspects a bacterial complication. The treatment that counts is early rehydration.
My cows are not sick: where does the virus come from?
Adults harbor and shed these viruses without becoming ill, particularly around calving. The calf therefore becomes contaminated in an apparently healthy herd.
Does vaccinating cows eliminate the problem?
The vaccine strengthens colostrum antibodies, but it only protects calves that drink colostrum early and in quantity. It does not replace calving hygiene or colostrum management.
Should the sick calf be isolated?
Yes. An affected calf sheds enormous quantities of virus and contaminates all the others. Isolate him, deal with him last and wash the equipment before returning to the healthy calves.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
ANSES — Agence nationale de sécurité sanitaire (France)
Content reviewed by the TunisieVet editorial team · Updated 09 August 2026
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