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Rumen bloat
The rumen constantly produces large quantities of gas. Normally, the cow expels them by burping. When this evacuation no longer takes place, the gas accumulates, the belly swells and compresses the lungs and the heart. Two very different si...
What is it?
The rumen constantly produces large quantities of gas. Normally, the cow expels them by burping. When this evacuation no longer takes place, the gas accumulates, the belly swells and compresses the lungs and the heart.
Two very different situations have the same name. In foamy bloat, the gas remains trapped in a stable foam which fills the rumen: the cow can no longer burp because there is no longer a pocket of free gas to evacuate. This is what typically happens when grazing young, moist legumes, alfalfa or clover, or with certain rations rich in finely ground concentrates.
In gas bloat, the gas is free but something blocks its exit: foreign body in the esophagus, stuck piece of beet or potato, animal lying on its side, paralyzed abdomen.
Key point
Vital emergency. A cow with a very distended left side that is breathing with its mouth open can die within minutes: call the veterinarian immediately and get the animal up.
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:
Swelling of the left flank, above, in the hollow in front of the hip: this is the warning sign. In advanced cases, both sides are distended and the back becomes rounded.
The cow stops eating and ruminating, becomes agitated, stomps, looks at its side, kicks towards the belly.
Rapid breathing, open mouth, tongue sticking out, neck stretched forward, profuse salivation.
If the esophagus is blocked, the cow struggles to swallow empty and drools a lot.
At the critical stage, the cow staggers, collapses, lies on its side and dies in a few minutes from asphyxiation.
Tapping the finger on the swollen left side produces a drumming sound in the gaseous form; the foamy form sounds more matte and full.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Putting out on young legumes, in regrowth, wet with dew or rain, on hungry animals which gorge themselves in a short time.
Rations rich in finely ground concentrates and low in long fibers, during fattening or during high lactation.
Foreign body blocked in the esophagus: piece of beet, potato, carrot, fruit, corn cob.
Any paralysis or slowing down of the rumen: milk fever, tetany, animal lying on its side, traumatic reticuloperitonitis, indigestion.
Compression of the esophagus by an abscess or mass in the thorax, a rarer situation.
In calves, swelling can also accompany improper or too rapid feeding.
Pastures rich in alfalfa, clover or other legumes, especially in spring.
Animals put out to grass on an empty stomach or after deprivation.
Grass wet from dew or a recent downpour.
Fattening cattle with lots of grain and little roughage.
Distribution of whole unsplit roots and tubers, or orchards accessible to animals.
Animal already sick, weakened, or lying down for a long time.
Individual sensitivity: some cows regularly bloat where their peers have nothing.
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 very bloated cow and in respiratory distress, there is no time for a lengthy examination: the veterinarian acts first and then examines.
He seeks to distinguish the foamy form from the gaseous form, because the course of action is not the same, and to identify an obstruction of the esophagus by passing a probe.
Once the emergency has passed, he looks for the underlying cause: ration, pasture, foreign body, underlying disease which has paralyzed the rumen.
A bloat that keeps recurring in the same animal should lead us to look for a mechanical cause or damage to the rumen, and not simply a ration problem.
Treatment
Inform the veterinarian immediately and describe the animal's condition precisely: the action depends on the degree of emergency.
In the meantime, get the animal up if it is lying down and make it walk gently: the movement sometimes helps to bring up the gas. Place it sideways, the front of the body higher than the back.
The veterinarian passes a probe through the mouth to the rumen: it evacuates the free gas and allows a foreign body to be identified and pushed back from the esophagus.
In the foamy form, it administers a product through this probe which breaks the foam and releases the gas.
In desperate cases, where the cow is dying of asphyxiation, a puncture of the left flank is necessary. It is an emergency veterinary procedure, potentially life-saving but fraught with consequences if carried out incorrectly: it can spill the contents of the rumen into the abdomen and cause fatal peritonitis. Don't improvise with a knife.
Never pour oil or liquid into the mouth of an animal in respiratory distress or drowsy: the product goes into the lungs.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Never put hungry animals on a plot rich in legumes. Have them eat hay before going out, and bring them in gradually, for a few tens of minutes the first day, then increasing.
Avoid putting out grass on pasture wet with dew or just after rain.
Prefer plots mixing grasses and legumes over pure stands of alfalfa or clover, and let the plant grow past the young stage before grazing.
Provide free-range hay in the plot during the transition period.
In rations rich in concentrates, keep a sufficient proportion of long fibers and avoid grinding too fine.
Split beets, potatoes and fruit before distribution, and fence the orchards.
Monitor the herd after each change of plot or ration: the first days are the most risky.
In animals that repeatedly bloat, discuss with your veterinarian an anti-foaming agent to include in the line during the at-risk period.
Possible complications
Death by asphyxiation and circulatory arrest, sometimes within a few minutes, in acute forms.
False swallowing and pneumonia if a liquid was administered to an animal that was no longer swallowing.
Peritonitis after a poorly performed flank puncture.
Inflammation of the rumen wall and repeated recurrence.
Injury or necrosis of the esophagus when a foreign body has been stuck there for a long time.
In animals rescued late, lasting digestive after-effects and reduced production.
When to see a veterinarian
The left flank is very distended and the cow is breathing quickly, with her mouth open: this is a life-threatening emergency, call immediately and don't waste any minutes.
She is drooling profusely and making efforts to swallow when empty: a foreign body is probably blocking the esophagus.
She lies on her side, staggers or refuses to get up even though her stomach is swollen.
Several animals swell at the same time after a change of plot: take the whole lot out and call.
An animal bloats repeatedly without an obvious cause: this deserves a cold examination.
Prognosis
Bloating caught early and relieved generally resolves well, and the animal eats again within a day.
Acute bloat with very distended flank and respiratory distress kills in a short time: the prognosis depends entirely on the speed of intervention.
Recurrence is common if the cause — pasture, ration, foreign body, rumen disease — is not identified and corrected.
Frequently asked questions
Can I pierce the side myself with a knife?
This gesture cannot be improvised. Done incorrectly, it spills the contents of the rumen into the abdomen and causes peritonitis which kills the animal more surely than bloating. Call the veterinarian, describe the emergency, get the animal up and walking while you wait.
Should you give oil to a bloated cow?
Not on your own initiative, and never to an animal in respiratory distress or lying down: it no longer swallows and the liquid passes into the lungs. The veterinarian administers anti-foam products by probe, directly into the rumen.
Why do my cows bloat especially in spring?
Because young and moist legumes, alfalfa and clover in the lead, produce a stable foam in the rumen which traps the gas. Starving animals released onto wet regrowth are in the riskiest situation.
How do I take my animals out on alfalfa without risk?
Have them eat hay before going out, wait until the dew has fallen, limit the first outing to a short time and increase gradually. Leave hay available in the plot and stay close to the herd for the first few days.
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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