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Hypomagnesemia
Hypomagnesemia is a sudden drop in magnesium in the blood. Magnesium calms the functioning of nerves and muscles: when it is lacking, everything goes out of control. Unlike other deficiencies, this one does not set in slowly. It kills withi...
What is it?
Hypomagnesemia is a sudden drop in magnesium in the blood. Magnesium calms the functioning of nerves and muscles: when it is lacking, everything goes out of control. Unlike other deficiencies, this one does not set in slowly. It kills within hours. A farmer may see a perfectly normal flock in the morning and find ewes dead or convulsing in the afternoon. It mainly affects lactating sheep placed on young, growing grass after spring or autumn rains. This magnificent herb is precisely the problem: rich in potassium and nitrogen, it prevents the body from absorbing magnesium. Sheep have practically no available reserves of magnesium: they depend on what they eat from day to day. This explains the brutality of the crisis. This is an absolute veterinary emergency, to be treated as such and not as a supplementation problem to be revisited later.
Key point
The Hypomagnesemia kills in a few hours, often the best lactating ewes, on spring grass which appears excellent. Faced with an animal that is trembling, staggering or convulsing, call the veterinarian immediately, remove the animal from the plot and do not attempt any injection on your own initiative: poorly administered magnesium stops the heart.
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:
At the beginning: nervous animals, on alert, who jump at the slightest noise, refuse to be approached, move away from the herd. Some become aggressive when they are usually calm.
Erected ears, fixed gaze, trembling of the muscles of the flanks, shoulders and eyelids.
Stiff and stilted gait, animal that raises its legs too high, staggers, stumbles.
Grinding of teeth, profuse salivation, foaming at the lips.
Unusual bleating, repeated cries for no reason.
Then sudden fall, animal lying on its side, head thrown back, legs pedaling, convulsions in attacks separated by phases of calm.
The slightest noise, a contact or an attempt to pick up the animal triggers a new attack: this is very characteristic.
Died within hours if nothing is done, sometimes faster.
In some herds, the only thing the farmer sees is a dead animal on pasture, in an area of trampled and plowed grass.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Consumption of young, growing grass, very rich in potassium and nitrogen, particularly after rain on fertilized or manured plots. Potassium directly interferes with the absorption of magnesium in the rumen.
Absence of mobilizable reserve: the magnesium in the bones of adult sheep is not quickly available, the animal depends on its daily diet.
Significant losses through milk in lactating females, especially those raising two or more lambs.
Triggering factors that push an already borderline animal over the edge: cold and humid weather, wind, a night without eating, transport, a change of plot, handling, even a short fast.
Ration low in fiber and energy, which accelerates transit and reduces absorption.
Associated calcium deficiency in certain cases, which complicates the picture and treatment.
Ewes in full lactation, especially those nursing several lambs: they are the ones who die.
Put out to grass on young regrowth after the spring or autumn rains.
Plots heavily fertilized with nitrogen and potash, or recently manured.
Cold, rainy and windy weather, which increases needs and reduces food intake.
Lack of roughage available, animals only eating young grass.
Any episode of fasting, even brief: transport, sorting, mowing, handling day, change of plot.
Elderly animals and animals in average condition.
Farms where the magnesium supplement is not put in place at the time of the risk, or not consumed by the animals.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The diagnosis is made in the field, based on the table and the context: lactating sheep, young grass, sudden crisis with convulsions. There is no time to wait for a lab result. The veterinarian quickly rules out other causes of convulsions and falls in sheep, which require different treatments: enterotoxemia, hypocalcemia, gestational toxemia, poisoning, nervous diseases. Some also associate themselves with the Hypomagnesemia. A blood test confirms the diagnosis afterwards and guides management for the rest of the herd. From a dead animal, a quick sample taken by the veterinarian can confirm the cause, which has enormous value in protecting other animals in the flock. Faced with a confirmed case, the entire group must be considered at immediate risk: this is the most important course of action.
Treatment
It's an emergency: the prognosis is decided in hours. Call the veterinarian immediately, without waiting to see the progress.
Treatment is based on the administration of magnesium salts, often combined with calcium, by a route and in a form chosen by the veterinarian. Magnesium administered directly into the vein is dangerous if misused: it can stop the heart. This is by no means something that the breeder should attempt alone.
No product, no dose and no route should be improvised from a bottle found on the farm or from a neighborhood tip.
While waiting for the veterinarian, the only useful thing is to reduce stimulation as much as possible: do not shout, do not run around the animal, do not try to pick it up by force, keep the dogs away. Noise and contact revive seizures.
Place the animal in a lying position on the sternum if possible without struggling, free its head, and prevent it from injuring itself on an obstacle.
As soon as a case occurs, the entire flock must be removed from the plot in question, with roughage made available and a supply of magnesium organized with the veterinarian for the following days. The movement is done calmly: rough handling can trigger a seizure in other animals.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Anticipate risky periods: putting young growth out to pasture, rainy spring, autumn after the first rains, ewes in full lactation.
Distribute a supply of magnesium throughout the risk period, in a form prescribed by the veterinarian and actually consumed by the animals. Magnesium is unpalatable: a block that no one licks protects no one.
Systematically make hay or straw available on plots of young grass, and let the animals use it before going out.
Avoid plots freshly fertilized with nitrogen and potash for lactating ewes.
Never leave animals fasting during risky periods: feed before transport, sorting or shearing.
Bring in or shelter animals during periods of cold, rain and wind.
Handle high-risk batches calmly, without dogs or rushing.
After a first case, consider the entire batch as threatened and organize prevention the same day, not the following week.
Possible complications
Death of the animal, often among the best dairy ewes in the flock.
Injuries and fractures during seizures.
Orphan lambs to raise, with all the workload and losses that this represents.
Recurrences in the same batch in the following days if the cause is not corrected: the first case is a warning.
Nervous sequelae in certain animals treated late.
Frequent association with a lack of calcium, which complicates management.
When to see a veterinarian
An animal is trembling, staggering, grinding its teeth or acting unusually nervous: call the veterinarian right away.
An animal is lying on its side, in convulsions, with its legs pedaling: it is a vital emergency, every hour counts.
A lactating ewe is found dead in the pasture on a regrowth of young grass: have the flock examined immediately, others are probably tipping over.
Several animals in the same batch appear nervous or stiff after a change of plot.
An animal becomes aggressive when it is usually calm.
After transport, shearing or a day of handling, lactating ewes show tremors.
Prognosis
Treated very early by the veterinarian, the animal can get up in a short time and recover completely: recoveries are sometimes spectacular.
An animal that has already been in convulsions for a while has a much more guarded prognosis, and some die despite correct treatment.
The risk of recurrence in the days that follow is high if breeding behavior is not modified: it is the entire flock that must be protected, not just the animal being treated.
Prevention is very effective: herds that are properly supplemented during periods of risk have practically no cases.
Frequently asked questions
My sheep are on beautiful grass, how can they lack anything?
It is precisely this grass that poses a problem. Young and growing, especially on fertilized plots, it is very rich in potassium, which prevents the absorption of magnesium. A superb herb can therefore kill lactating sheep within a few hours.
Can I give an injection myself while waiting for the vet?
No. Magnesium administered directly into the vein can stop the heart if misdirected. It's a veterinary gesture. In the meantime, the only useful help is to leave the animal in absolute calm, without noise, without a dog and without trying to force it up.
A sheep died, should I worry about the others?
Yes, immediately. One case means that the entire batch is exposed to the same conditions. The animals must be taken out of the plot, given them roughage and magnesium supplementation arranged with the veterinarian on the same day.
Is a magnesium licking block enough?
Only if it is actually consumed, which is not a given: magnesium tastes bad and many blocks remain intact. Check for hollowing, and talk to the vet about a more reliable form for high-risk times.
References
FAO — Organisation des Nations unies pour l'alimentation et l'agriculture
ANSES — Agence nationale de sécurité sanitaire (France)
Content reviewed by the TunisieVet editorial team · Updated 11 August 2026
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