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Oak acorn poisoning
Acorns, young leaves and buds of oak contain tannins in large quantities. Consumed in small quantities, they are of no consequence: sheep have always collected them under oak trees. The problem appears when they become a significant part of...
What is it?
Acorns, young leaves and buds of oak contain tannins in large quantities. Consumed in small quantities, they are of no consequence: sheep have always collected them under oak trees.
The problem appears when they become a significant part of the ration. The tannins then damage the digestive wall and especially the kidneys, which end up no longer filtering.
Two situations create the risk. In autumn, a gust of wind or a storm causes a mass of acorns to fall at once, and the animals, who appreciate them, gorge themselves on them. In spring, it is the young leaves and buds, even richer in tannins, which pose a problem.
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:
The first signs appear a few days after the start of heavy consumption.
Despondency, animal which stays behind, loses its appetite, stops ruminating.
Marked constipation at first, with hard, dry, dark droppings, sometimes covered with mucus or blood.
Then diarrhea, often dark and smelly, which replaces constipation.
Significant thirst and scanty urine: the animal drinks a lot and urinates little, which indicates kidney damage and constitutes the most important signal.
Dehydration despite drinking.
Soft swellings under the jaw, under the stomach and in the limbs, linked to kidney damage.
Rapid weight loss, weakness, animal ending up lying down.
Unusual smelling breath and urine.
In severe forms: complete cessation of urine and death within a few days.
Several animals in the flock are generally affected, to varying degrees.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Heavy and prolonged consumption of acorns, young leaves or oak buds.
Massive falls of acorns after a gust of wind, a storm or during years of high production: the animals gorge themselves within a few hours.
Lack of grass and fodder, which pushes the herd to fall back on what is available under the oak trees. This is the determining factor: with a correct ration, sheep do not consume enough acorns to become poisoned.
Wooded areas or plots lined with oak trees, grazed in autumn or at spring bud break.
Hungry animals released into an area rich in acorns.
Unaccustomed animals: those who live permanently under oak trees seem to tolerate them better than those who suddenly discover the resource.
Lack of water, which aggravates kidney damage.
Courses and plots with oak trees, grazed in autumn.
Years of high acorn production.
Episodes of wind or storm causing the acorns to fall en masse.
Budburst in spring, with young leaves and buds very rich in tannins.
Fodder shortage, end of dry season, years of drought.
Animals starved or released unfed.
Insufficient watering.
Young animals and newly introduced animals in a wooded area.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The context is decisive: tell the veterinarian that your animals have access to oak trees and that there has been a significant fall of acorns or recent budburst.
The veterinarian examines the general condition, dehydration, swelling, and asks about the quantity of urine emitted.
Blood tests assess the functioning of the kidneys: this is the most useful test to assess the severity and decide what can be tried.
A urine analysis completes the assessment.
Examination of a dead animal shows characteristic lesions of the kidneys and digestive tract, and makes it possible to assess the risk for the rest of the batch.
The veterinarian rules out other causes of kidney damage and digestive problems in the sheep, including other poisonings and the ram's urinary obstruction, which is a completely different surgical emergency.
An animal that is not urinating should be seen quickly, regardless of the cause.
Treatment
There is no antidote: treatment aims to support the animal while the kidneys recover, if they still can.
The first measure, immediate and free, is to remove the entire lot from the oak area and provide good quality fodder and plenty of clean water.
The veterinarian sets up rehydration, often by infusion, and management of kidney and digestive damage. Products limiting the absorption of tannins in the digestive tract can be used on prescription.
No product should be administered by the breeder: purges and oils given on their own initiative worsen the condition of a dehydrated animal.
A diet rich in fiber and energy, fed ad libitum, helps the rumen to recover and distracts animals from acorns.
Affected animals must be kept quiet, sheltered, with easy access to water, and monitored daily.
The rest of the batch must be monitored for several days: they all ate the same thing, to varying degrees.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Do not graze oak rangelands during periods of massive acorn fall, nor when young leaves are bursting.
Monitor episodes of wind and storm in autumn: it is often the next day that accidents occur.
Ensure a correct basic ration of fodder and energy: a satiated herd does not eat enough acorns to become poisoned. This is the most effective measure.
Distribute hay before taking the animals out to a wooded plot, and never release them hungry.
Rake or fence off areas where acorns accumulate, when possible.
Guarantee abundant watering, which protects the kidneys.
Monitor the animals in the days following access to an oak grove, observing whether they urinate normally.
Ask the veterinarian for an opinion on supplements limiting the effect of tannins in farms that cannot avoid oak groves.
Possible complications
Permanent renal failure in the most affected animals, with animals never returning to their condition.
Death due to cessation of kidney function.
Severe dehydration and general weakening.
Long-lasting weight loss and loss of production throughout the season.
Abortions in pregnant females.
Multiple losses in the same batch when the whole troop has had access to the acorns.
When to see a veterinarian
Your animals have had access to a large fall of acorns and several are killed.
An animal drinks a lot but urinates very little or not at all: call immediately.
Hard, black droppings, sometimes with blood, appear in many animals.
Soft swellings form under the jaw, under the stomach or on the limbs.
An animal loses weight quickly and remains lying down.
Animals die a few days after a stay in an oak grove.
Prognosis
Mild forms, spotted early and removed from the area in time, recover well within a few days to a few weeks.
Animals whose kidneys are already seriously damaged, which no longer urinate and show swelling, have a poor prognosis despite treatment.
Some survivors remain in kidney failure and never regain their performance.
At the herd level, the prognosis is good as long as access is removed and the basic ration is corrected: it is a management problem before being a medical problem.
Frequently asked questions
My sheep have been eating acorns for years without a problem, why now?
Because it's not the glans itself that is the problem, but the quantity. A massive fall after a storm, or a lack of grass that causes the herd to eat only that, turns a harmless habit into poisoning. The context of the year matters more than the presence of oaks.
Should I cut down all my oak trees?
No. The effective measure is to manage access and above all to feed the animals well: a satiated herd consumes acorns in innocuous quantities. We simply avoid wooded plots during massive falls and at spring bud break.
My sheep drinks a lot but hardly urinates anymore, is this serious?
Yes, this is the most serious sign of this poisoning: it indicates kidney damage. Call the veterinarian without delay, because it is at this stage that treatment can still change the outcome.
Are young oak leaves in spring dangerous too?
Yes, and they are even richer in tannins than acorns. Spring bud burst is a second risky period, often forgotten because we associate this intoxication only with autumn.
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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