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Weathering
Weathering, which breeders simply call bloat, is the accumulation of gas in the rumen, the large fermentation pocket that occupies the entire left flank of the sheep. A healthy ruminant constantly produces gas and releases it by burping sev...
What is it?
Weathering, which breeders simply call bloat, is the accumulation of gas in the rumen, the large fermentation pocket that occupies the entire left flank of the sheep. A healthy ruminant constantly produces gas and releases it by burping several times per minute. When this mechanism is blocked, the rumen swells like a balloon in a few hours and crushes the lungs and the large vessels of the stomach. The animal does not die from its stomach: it dies from suffocation. We distinguish two forms. Foamy Weathering, the most common in pasture: the gases remain trapped in a stable foam that the animal cannot burp up. Gaseous Weathering, where it is the passage itself which is blocked, for example by a piece stuck in the esophagus or in a lying animal which can no longer burp. In both cases, it is a vital emergency which is measured in hours, sometimes less. A sheep found bloated in the morning may be dead before noon. This is one of the rare situations where the call to the veterinarian cannot wait until after the tour.
Key point
A swollen, tense and sonorous left flank in a sheep is a vital emergency that can be counted in hours. Call the veterinarian right away and immediately remove the remaining batch of the offending forage.
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 left flank swells, fills out, then exceeds the line of the back. The hollow that normally exists just in front of the hip fades, then bulges.
The wall becomes hard and tense like a drum skin: by tapping with your fingertips, you obtain a hollow and sonorous sound, very different from the dull noise of a normal stomach.
The animal stops ruminating and refuses to eat.
He is worried: he gets up, lays down again, stomps around, looks at his side, paws at his stomach, moans.
He drools, cranes his neck, breathes quickly, often with his mouth open and his nostrils dilated.
He urinates and defecates frequently at first, then nothing.
At an advanced stage, he staggers, collapses, rolls onto his side with his tongue sticking out, and dies within minutes.
The gaseous form is often accompanied by signs of obstruction: swallowing efforts, coughing, flowing saliva, regurgitation.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Foamy Weathering is caused by forages rich in soluble proteins which foam the contents of the rumen: young and moist legumes such as alfalfa, clover or berseem, regrown after a rain, young budding cereals. Rations very rich in finely ground concentrate, without long fiber, produce the same effect in sheepfolds. The risk is greatest when animals arrive hungry on a plot and eat quickly and in large quantities, particularly on grass wet from dew, rain or irrigation. Gaseous Weathering has other origins: a foreign body blocked in the esophagus, such as a piece of beet or a fruit swallowed whole, inflammation or compression of the esophagus, paralysis of the rumen, or quite simply an animal lying on its back or stuck against a wall, which can no longer burp. Certain nervous diseases and certain poisonings block the movements of the rumen and are first manifested by bloating: this is why an animal which bloats without dietary reason must be examined. A bottle-fed lamb can also bloat when milk, drunk incorrectly or given too quickly, passes into the rumen instead of going directly to the abomasum.
Put out to grass on alfalfa, clover or berseem, especially in spring and on irrigated plots.
Animals released hungry, on empty stomachs, on palatable fodder.
Grass wet from morning dew, rain or recent irrigation.
Rations rich in finely ground cereals, with no hay or straw available.
Sudden changes in ration, plot or feed supplier.
Animals lying down for a long time, weakened, at the end of pregnancy or injured, which no longer burp normally.
Distribution of roots and whole fruits, classic cause of gaseous form.
Animals that have already bloated once: some recur for anatomical or nervous reasons.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Faced with a swollen animal, the veterinarian acts first and then looks for the cause: he assesses breathing, the state of consciousness and the tension of the flank to decide whether to decompress immediately. He passes a flexible probe through the mouth to the rumen. This gesture has a double value: it evacuates the free gases, and if almost nothing comes out while the animal is very bloated, it points towards foam or an obstruction of the esophagus. The probe also makes it possible to check that the passage is free. He examines the rumen juice brought back by the probe: its odor, color and consistency help to distinguish a simple Weathering from ruminal acidosis or alkalosis. He palpates the neck groove looking for a foreign body. When several animals are affected or when an animal relapses, he examines the ration, the plots and the method of distribution: the cause is almost always in the breeding management, not in the animal. An autopsy on a dead animal makes it possible to confirm and above all to prevent the rest of the batch from following.
Treatment
It's an emergency: call the veterinarian immediately, describing the swollen, tense and sonorous left flank. Do not procrastinate and do not go to the village to find a remedy while the animal is suffocating.
In the meantime, a few simple actions help without risk: get the animal up and walk slowly, place it on a slope with the front end raised to clear the diaphragm, and above all remove all the rest of the lot of fodder in question.
The veterinarian evacuates gas using a probe when possible. Against the foam, he administers an anti-foam product through this same probe which bursts the bubbles and releases the gas in one go; the effect is often spectacular.
In desperate situations, when the animal is about to die of suffocation, he pierces the rumen on the left side with a trocar to let the gas out. This gesture saves the animal but exposes it to a stomach infection: it is carried out in clean conditions and is followed by treatment. This is not an action to be improvised with a knife: animals die every year from peritonitis after an attempt made on the farm.
Never force an animal to drink if it is bloated and unable to breathe: the liquid goes into the lungs and causes pneumonia, which is often fatal.
After the crisis, the animal needs rest, coarse hay, clean water and a gradual resumption of the concentrate; the rumen takes several days to return to normal functioning.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Never release hungry animals onto alfalfa, clover or berseem: distribute coarse hay or straw first, so that they arrive with their bellies already occupied.
Wait until the dew has lifted and the grass has dried before putting the animals on a legume; avoid entry immediately after rain or irrigation.
Start with short grazing times and gradually increase them over several days, staying close to the flock for the first two hours, which are the riskiest.
Always keep long fiber available in rations rich in concentrate, and do not feed finely ground cereals alone.
Respect progressive transitions with each change of ration, plot or batch of feed.
Cut the roots and fruits distributed into pieces, to avoid the gaseous form by obstruction.
Particularly monitor the herd in spring, when vegetation resumes, and on irrigated plots.
Identify animals that repeatedly bloat: they must be examined, and sometimes reformed.
Keep the veterinarian's number posted at the sheepfold: with this disease, the time spent looking for it is simply wasted time.
Possible complications
Death from suffocation, often within a few hours, sometimes in less than an hour in acute forms.
Regurgitation of rumen contents and passage into the lungs, with false swallowing pneumonia.
Peritonitis after trocardization carried out in poor hygienic conditions.
Prolonged shutdown of the rumen after the attack, with loss of appetite and weight loss for several days.
Recurrence as long as the ration or grazing method has not been corrected, sometimes with several animals lost in the same week.
Abortion or pregnancy toxemia in a ewe at the end of pregnancy having suffered a seizure.
When to see a veterinarian
An animal's left side is swollen, tense, and sounds hollow when tapped: call immediately, it's a life-threatening emergency.
The animal breathes quickly, with its mouth open, or cranes its neck to breathe.
He can't sit still, looks at his side and kicks his paws towards his stomach.
He drools and struggles to swallow: an obstruction of the esophagus may be to blame.
He is lying on his side and does not get up.
Several animals from the same batch swell after being put out to grass or a change of ration: remove the entire batch of the fodder in question and call.
An animal repeatedly bloats for no obvious dietary reason.
Prognosis
Decompressed in time, a bloated animal often recovers very quickly and returns to normal behavior within a few hours. This is one of the most rewarding emergencies when caught early.
After a certain stage, when the animal is lying down, tongue out and breathing very labored, the prognosis becomes poor even with immediate decompression.
At the batch level, everything depends on correcting the cause: as long as the fodder or ration in question remains distributed, other animals will follow in the following hours or days.
Frequently asked questions
My sheep is swollen on the left side, how much time do I have to spare?
Very little: a few hours, sometimes less if the swelling is rapid and breathing is difficult. The rumen compresses the lungs and the animal dies of suffocation. Call the veterinarian right away, get the animal up and walk gently while you wait.
Can I pierce the side myself with a knife?
This gesture exists, but it is reserved for the veterinarian and for situations where the animal is about to die. Done with a dirty knife and in the wrong place, it causes a stomach infection which kills the animal after relieving it. Call first: in the vast majority of cases, a probe is enough.
Can I give him some oil or medicine to help it pass?
No. An animal that is bloated and has difficulty breathing swallows poorly: the liquid goes into the lungs and causes pneumonia, which is often fatal. The veterinarian administers anti-moss products through a probe, which is safe and much more effective.
How can we prevent this from happening again when putting it out to grass?
Distribute hay or straw before taking the animals out, wait until the dew has lifted, start with short outings and extend them over several days. Pasture bloat is almost always a driving error, not inevitable.
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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