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Milk fever
Despite its name, milk fever is not an infection and is not accompanied by fever: on the contrary, the temperature is often lower than normal. It is a sudden drop in calcium in the blood, almost always around calving. At the start of lactat...
What is it?
Despite its name, milk fever is not an infection and is not accompanied by fever: on the contrary, the temperature is often lower than normal.
It is a sudden drop in calcium in the blood, almost always around calving. At the start of lactation, the udder suddenly requires a large quantity of calcium to produce colostrum and then milk. If the cow's body does not mobilize its bone reserves and calcium from the ration quickly enough, the blood level plummets.
Calcium makes muscles work. Without it, the cow weakens, staggers, then lies down and can no longer get up.
Key point
Veterinary emergency. A lying cow that does not get up after calving must be seen without delay: each hour spent on the ground worsens the prognosis.
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:
Signs most often appear in the hours following calving, sometimes just before.
First phase, brief and often unnoticed: the cow is agitated, refuses to eat, tramples, trembles, walks stiffly and staggers.
Second phase, the most typical: the cow is lying on its sternum, its head turned towards its side. The muzzle is dry, the gaze is fixed, the ears and the base of the horns are cold to the touch. She tries to get up and can't.
Dung becomes scarce, the rumen slows down, bloating can set in because the cow no longer ruminates or belches.
Third phase: the cow tips onto its side, no longer reacts, breathes poorly. This is a critical stage.
Milk production immediately drops and the cow can no longer be milked normally.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The direct cause is the lack of calcium available in the blood when lactation begins.
The mechanisms that draw calcium from the bones and absorb it in the intestine take some time to activate. In a cow whose dry ration was already rich in calcium, these mechanisms are “asleep” and do not respond quickly enough.
An excess of potassium in the end-of-gestation ration, common with certain fertilized forages, disrupts the animal's acid-base balance and partially blocks calcium mobilization.
A lack of magnesium also interferes with calcium regulation.
Aging plays a role: the more lactations a cow has behind her, the less quickly she mobilizes her bone reserves.
Adult cows, generally from the third lactation; heifers are rarely affected.
High producers and specialized dairy breeds, whose demand for calcium at calving is the highest.
Drying ration too rich in calcium or potassium, fodder not analyzed.
Cows that are too fat at calving, which eat little around birth.
History of milk fever during a previous calving: the risk repeats itself.
Difficult calving, twins, or any concomitant illness that reduces appetite.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian makes the diagnosis based on the clinical examination and the context: adult cow, recent calving, animal lying down, cold extremities, normal or low temperature.
He checks the frequency and strength of the heartbeat, the condition of the stomach, the position of the head and the ability to get up.
A blood test can confirm the drop in calcium and at the same time look for a lack of magnesium or phosphorus, which changes the course of action to take.
It especially rules out other causes of cow lying down after calving: nerve or muscle injury during birth, hip dislocation, serious mastitis, uterine infection, ketosis, lack of magnesium. Several of these problems can also coexist.
The response to treatment is part of the diagnosis: a cow that recovers quickly after calcium correction confirms the hypothesis.
Treatment
Treatment is the sole responsibility of the veterinarian and must be started without delay.
It is based on the supply of calcium by vein, administered slowly and under monitoring of the heart: given too quickly, calcium can cause cardiac arrest. This is why a breeder should never perform an intravenous calcium injection himself.
An oral relay is often prescribed afterwards to avoid relapse, sometimes supplemented with magnesium or phosphorus depending on the results of the examination.
While waiting for the veterinarian, place the cow on thick, non-slippery bedding, in a sternal position, with her head raised and supported so that she does not tip onto her side.
Never pour liquid or oral solution into the mouth of a sleeping cow: she no longer swallows properly and the liquid goes into the lungs.
If the cow remains lying down, it must be turned from one side to the other several times a day to prevent the weight of the body from crushing the muscles and nerves, with water and fodder within easy reach.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention takes place during the last weeks of gestation, not at calving.
Have the fodder intended for dry cows analyzed: this is the only way to know their calcium and especially potassium content. Forages highly fertilized with potash should be reserved for lactating cows.
A dry ration low in calcium forces the body to keep its mobilization mechanisms alert, ready to function from calving.
Anionic salts, which slightly acidify the body at the end of gestation, are an effective but technical tool: they are set up with the veterinarian or the nutrition advisor, with control of the result, never by judgment.
Ensure a correct magnesium intake throughout the drying period.
Avoid fattening dry cows: a cow that is too fat eats less just before calving and starts its lactation in debt.
In cows that have already had milk fever, an oral intake of calcium at the time of calving can be prescribed as a preventative measure; its form and timing are defined by the veterinarian.
Monitor freshly calved cows closely: the earlier the disorder is detected, the more easily it is corrected.
Possible complications
The muscles and nerves compressed by the weight of the animal are damaged when the cow remains lying down for a long time: she may then no longer get up even once the calcium has been corrected. This is the lying cow syndrome, with a much poorer prognosis.
False swallowing and pneumonia if attempting to water or drain a drowsy cow.
Bloating of the rumen in a cow lying on its side, which can no longer belch.
The drop in calcium also relaxes the muscles of the uterus and the teat sphincter: retained placenta, infection of the uterus, mastitis are more frequent afterwards.
It promotes ketosis and the movement of the abomasum, because the cow eats less and its rumen slows down.
Relapse in the days that follow, classic and to be anticipated.
When to see a veterinarian
A cow that has just calved is lying down and does not get up: call immediately, it is an emergency.
She staggers, shakes, walks stiffly or refuses to move in the hours after giving birth.
Her ears and the base of her horns are cold even though she does not have a fever.
She has her head turned to her side and her gaze is fixed.
She is tilted on her side and bloated: the prognosis is decided in minutes.
She got up after a first treatment and went back to bed: warn immediately.
Prognosis
Treated early, the vast majority of cows recover and resume normal lactation.
The prognosis depends above all on the time spent lying down: a cow taken into care within an hour recovers well, a cow left immobilized for half a day or more risks irreversible muscle damage.
Relapses within the first two days are common and do not mean treatment has failed.
A cow that has had milk fever remains more exposed to other problems at the start of lactation: it deserves closer monitoring for several weeks.
Frequently asked questions
Why do we speak of “fever” when the cow does not have a fever?
It is an old name, inherited from the time when this disorder was confused with a calving infection. In reality the temperature is normal or low, and the ears are cold. It's a lack of calcium, not a microbe.
Can I give the calcium injection myself?
No for the venous route. Injected too quickly, calcium can stop the heart, and the procedure requires monitoring of the heart rate throughout the administration. Only the veterinarian should do this. However, he can prescribe oral intake to you to use in a specific context.
Why should you not give a lying cow something to drink?
Because a weakened cow no longer swallows properly: the liquid passes into the trachea and causes pneumonia, which is often fatal. Leave the water within his reach but do not pour it into his mouth.
How can we prevent this from happening again at the next calving?
By working on the drying ration: fodder analyzed, calcium and especially potassium intake controlled, sufficient magnesium, cows neither too fat nor undernourished. This is a point to review with your veterinarian, because a cow that has already had milk fever will do so again if nothing changes.
Are heifers affected?
Very rarely. The risk increases with the number of lactations, because bone calcium mobilization mechanisms become less responsive with age.
References
FAO — Organisation des Nations unies pour l'alimentation et l'agriculture
Content reviewed by the TunisieVet editorial team · Updated 09 August 2026
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