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Ruminal acidosis
The rumen, or rumen, is a huge fermentation tank populated with microbes that digest fiber for the cow. This flora works in a low-acid environment and takes time to adapt to a change in diet. When the cow suddenly swallows a large quantity...
What is it?
The rumen, or rumen, is a huge fermentation tank populated with microbes that digest fiber for the cow. This flora works in a low-acid environment and takes time to adapt to a change in diet.
When the cow suddenly swallows a large quantity of foods rich in starch or sugars - cereals, bread, flour, beets, fruit, factory leftovers - fermentation goes into overdrive, acid accumulates and the environment becomes too acidic. Useful microbes die, others proliferate.
There is an acute, brutal and sometimes fatal form, which follows accidental access to cereals, and a subacute, more insidious form, linked to a daily ration too rich in concentrates and too poor in effective fiber.
Key point
An accidental grain overload is a veterinary emergency: the condition can deteriorate within a few hours, and several animals are often affected at the same time.
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:
In the acute form, signs appear within a day after ingestion.
Complete cessation of eating and rumination, silent and swollen rumen, filled with sloshing liquid contents.
Profuse diarrhea, clear, foamy, with a sour odor, sometimes containing undigested grains.
Rapid dehydration, sunken eyes, dry muzzle.
Despondency, staggering gait, cow that lies down and ends up not getting up again.
In severe cases, the cow remains prostrate, the temperature is low and the condition deteriorates within a few hours.
In the subacute form, nothing spectacular: production drops, the milk fat level drops, the dung is soft, yellowish, foamy, sometimes with grains or bubbles. Cows ruminate less, eat in spurts, limp more and more often and lose weight. Grinding teeth reflects digestive discomfort.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Sudden ingestion of a large quantity of foods rich in starch or rapidly fermentable sugars.
Accidental access to the silo, the grain storage room, a ripped bag, bakery leftovers or factory deviations.
Lactation ration too rich in concentrates compared to fiber, or concentrates distributed in a single meal rather than distributed.
Fodder that is too finely chopped or too low in long fibers: the cow ruminates less, salivates less, and saliva is precisely what buffers the acidity of the rumen.
Sorting at the trough: the cow eats the fines and concentrates first and leaves the fibers, which unbalances its actual ration even if the calculated ration is correct.
Food transition too rapid, particularly when putting out to grass, closing the silo or starting fattening.
Cows at the beginning of lactation, in which concentrates rise quickly.
Fattening cattle receiving a lot of grain.
Storage of grains accessible to animals: this is the most common cause of accidents.
Only one daily distribution, insufficient trough, cows rushing for the ration after an empty one.
Forage chopped too short, ration too wet or too dry which favors sorting.
Animals not accustomed to concentrates, or resumption of distribution after an interruption.
Heat: in high temperatures, the cow eats less often but more quickly, which accentuates the fermentation jolts. The context is common in summer in the Maghreb.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian finds out precisely what the animal has eaten and since when: this is the most useful element for the diagnosis.
It examines hydration status, temperature, heartbeat, rumen filling and sounds.
An analysis of the contents of the rumen, taken by probe, makes it possible to assess its acidity and the state of the flora.
A blood test assesses the general impact and dehydration.
In the subacute form, the diagnosis is made at the herd level: observation of droppings, time spent ruminating, milk levels, number of lamenesses, examination of the ration actually consumed and refusals.
Treatment
The acute form is an emergency: the earlier treatment is received, the better the chances.
The veterinarian seeks to evacuate or neutralize the acidic contents of the rumen, to rehydrate the animal by perfusion and to correct the acidification of the body.
Washing the rumen by probe, or even surgical intervention to empty it in extreme cases, may be decided.
Tampons, anti-inflammatories, sometimes antibiotics or transfaunation – that is to say the addition of flora taken from a healthy cow – are used depending on the situation, on veterinary decision.
Immediately remove access to the food in question and check if other animals may have consumed it: cases often occur in groups.
Offer good quality hay and clean water, and do not administer anything by mouth to a slaughtered animal on your own initiative.
In the subacute form, there is no miracle individual treatment: correction requires ration and feeding, and damaged feet must be trimmed and cared for.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Close access to inventory. An open silo, a grain room without a door or a bag left in a corridor are enough to cause a serious accident.
Carry out any dietary transition gradually, over several days at least, by increasing concentrates in small increments.
Keep enough long and effective fibers in the ration: this is what makes you ruminate, salivate and stamp the rumen.
Spread the concentrates over several meals rather than one massive intake; a mixed and homogeneous ration limits sorting.
Avoid periods without food at the trough, which cause the next distribution to eat too quickly.
Monitor droppings, rumination time and milk levels: these are the best early indicators of herd acidosis.
Ensure sufficient space at the trough for dominated cows to eat calmly, and clean water at all times.
Review the ration with your veterinarian or a nutrition advisor as soon as lameness increases or the milk fat content drops.
Possible complications
Laminitis and lameness: acidosis damages the tissues of the foot and results, weeks later, in painful and deformed hooves.
Inflammation of the lining of the rumen, which allows bacteria to pass to the liver and causes liver abscesses.
Bloat, displacement of abomasum, chronic diarrhea.
Long-term decline in milk production and rates, poor recovery, degraded fertility.
In severe acute forms, brain damage, major dehydration and death of the animal despite treatment.
Cows that survive severe acute acidosis often remain with poorly functioning rumens and may need to be culled.
When to see a veterinarian
One or more animals have had access to cereals, bread or concentrates in quantity: call without waiting for the first signs.
A cow suddenly stops eating and ruminating, its rumen no longer makes noise.
Profuse and sour diarrhea with visible grains.
Dehydrated animal, staggering, lying down and unable to get up.
In the herd: soft and foamy dung in several cows, drop in fat content, increasing lameness.
Prognosis
The acute form is serious: animals treated very early often recover, those which are already lying down and dehydrated have a guarded prognosis, even with intensive treatment.
Complete recovery of the rumen flora requires several days to a few weeks, with a gradual increase in production.
The laminitis that follows can leave permanent after-effects on the hooves.
The subacute form is corrected well when the ration and feeding habits are reviewed, but the damage to the feet takes a long time to disappear.
Frequently asked questions
My cows forced the door of the grain room last night, what should I do?
Call the veterinarian immediately, even if the animals appear normal. The signs appear a few hours late and early treatment changes everything. Remove access, count affected animals and offer hay and clean water.
How do I know if my herd is in acidosis without doing an analysis?
Look at the dung (soft, foamy, with grains or bubbles), count the cows that ruminate when the herd is at rest, follow the milk fat content and the number of lamenesses. These clues, taken together, are very telling.
Is bicarbonate enough to solve the problem?
A tampon helps, but it does not replace a correct ration. If the cow does not ruminate enough due to lack of effective fiber, or if she sorts at the trough, acidosis will return. The buffer accompanies the correction of the ration, it does not replace it.
Why does lameness appear a long time later?
Because acidosis damages the production of the horn of the foot. The damage then descends with the growth of the hoof and only becomes visible several weeks later. A wave of lameness therefore provides information on what happened at the trough one or two months earlier.
References
FAO — Organisation des Nations unies pour l'alimentation et l'agriculture
EFSA — Autorité européenne de sécurité des aliments
Content reviewed by the TunisieVet editorial team · Updated 09 August 2026
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