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Sheep pasteurellosis
Pasteurellosis is the main cause of pneumonia in sheep and one of the leading causes of mortality in weaned and fattened lambs. The causative bacteria are often already present in the noses and throats of healthy animals. They only become d...
What is it?
Pasteurellosis is the main cause of pneumonia in sheep and one of the leading causes of mortality in weaned and fattened lambs.
The causative bacteria are often already present in the noses and throats of healthy animals. They only become dangerous when a constraint weakens the animal: transport, sudden change of diet, weaning, mixing of batches, poor ventilation, cold or heat stroke, other illness.
They then descend into the lungs and cause pneumonia which progresses quickly.
Key point
Veterinary emergency. Every hour counts: a lamb that breathes quickly and refuses to eat must be seen the same day.
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:
High fever, downed animal that pulls away and refuses to eat.
Rapid, shallow breathing, flapping sides; the animal cranes its neck and breathes with its mouth open in severe cases.
Cough, sometimes discreet, discharge from the nose first clear then thick.
Animal that remains lying down and does not get up, or gets up with difficulty.
Lamb who lets himself be caught easily even though he was fleeing the day before: this detail should raise alarms.
In the peracute form: rapid death, within a few hours, with few or no prior signs.
In chronic forms: slowed growth, persistent cough, animals that never catch up.
The forms of the newborn lamb also exist, with despondency and rapid death.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The bacteria in question belong to the pasteurella group, mainly Mannheimia haemolytica, as well as Bibersteinia trehalosi and Pasteurella multocida.
These bacteria normally live in the upper respiratory tract without causing illness.
A triggering factor disrupts this balance: stress, prior respiratory virus, dust and ammonia in the building, parasitism, deficiency.
The bacteria then multiply and spread to the lung, where they cause widespread inflammation and the release of toxins.
Transportation and handling: The disease is so often linked to transportation that it has taken on the popular name “transport fever.”
Weaning, sudden change of ration, fattening.
Mixture of animals of different origins in the same batch.
Poorly ventilated, overcrowded, humid buildings loaded with dust and ammonia.
Sudden temperature variations, drafts, extreme heat.
Pre-existing viral or parasitic respiratory infections.
Poorly immunized lambs, having received too little colostrum.
Transmission
Between animals by droplets emitted when coughing and sneezing, and by secretions from the nose.
By direct nose-to-snout contact, at the trough and at the drinker.
The disease often occurs within a few days of transport, weaning, batch mixing or a change of house.
Sharing the same poorly ventilated room, with high density and litter loaded with ammonia, strongly encourages diffusion.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian examines the lungs, takes the temperature and examines the entire group, because affected animals are rarely isolated.
He takes stock of recent events: transport, weaning, change of food, arrival of new animals, state of ventilation.
In the event of mortality, an on-site autopsy provides decisive information: it directs the diagnosis much better than guesswork and allows management to be adapted for the rest of the herd.
Samples can be sent to the laboratory, in particular to identify the bacteria and test its sensitivity to antibiotics: this is particularly useful when several treatments have already failed.
Treatment
Treatment is emergency: it is based on antibiotics prescribed by the veterinarian, administered as soon as possible. An animal treated at the first signs has a good chance of recovery; treated late, it often leaves damaged lungs.
Anti-inflammatories are frequently combined to reduce fever and limit lung inflammation, upon prescription.
Sick animals must be placed in a quiet, well-ventilated area without drafts, with easy access to water and palatable food.
When several animals from the same batch are affected, the veterinarian can decide on action at the batch level: only he can judge.
Waiting times for meat and milk must be respected.
Never treat on your own initiative with an antibiotic left over from a previous episode: the wrong product wastes decisive hours and promotes resistance.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Reduce constraints around sensitive periods: do not combine transport, weaning and change of diet in the same week.
Take care of the ventilation of buildings: renewed air without a cold draft on the animals, dry litter, an odor of ammonia which does not hit the throat when you enter.
Limit density, avoid mixing animals of different origins.
Ensure good colostrum intake in lambs in the first hours of life.
Monitor batches after each transport or change, and identify animals that isolate themselves early.
Control parasitism and diet, which determine the resistance of young people.
Promptly isolate any animal that is coughing or breathing poorly.
Vaccination
Vaccines against pasteurella exist and are widely used in sheep farming, often combined with protection against enterotoxemia in the same product.
They fit into a schedule: vaccination of ewes before lambing to protect the lambs with colostrum, then vaccination of the young. The exact schedule is established by the veterinarian according to the management of the herd and the risk period.
Protection is never total: vaccination reduces the frequency and severity of cases, it does not replace good ventilation or limiting constraints.
Vaccinating an animal that is already sick is useless: vaccination is an anticipation measure.
Possible complications
Rapid death in peracute forms, even before treatment can act.
Permanent lung damage in survivors: animals out of breath, which gain weight poorly and lag behind.
Pleurisy and lung abscesses, with seizure of the carcass at the slaughterhouse.
Relapses following a new constraint.
Serial losses in a feedlot when the source of stress is not corrected.
When to see a veterinarian
A lamb is breathing quickly, its sides flapping, or breathing with its mouth open: call immediately.
An animal is slaughtered, feverish, refuses to eat and isolates itself from the crowd.
Many animals cough in the days following transport, weaning or mixing batches.
An animal is found dead without prior signs: have the corpse examined rather than discarding it, this protects the rest of the herd.
A treated animal does not improve within the time frame announced by the veterinarian.
Prognosis
Treated within the first hours, pneumonia progresses favorably in a good number of cases.
Treated late, it leaves pulmonary after-effects: lost growth, animals which will not catch up.
The acute forms are often fatal despite everything.
At the batch level, the prognosis depends above all on the correction of the causes: as long as ventilation, density or weaning management do not change, cases repeat themselves.
Frequently asked questions
Why do my lambs get sick right after transport?
Transport combines stress, dust, promiscuity and fasting. Bacteria already present in the respiratory tract take advantage of this to descend into the lungs. This is why we speak of “transport fever” and why we must closely monitor the batches in the days following arrival.
An animal found dead without having shown anything, is that possible?
Yes, it is even characteristic of hyperacute forms. Have the body examined by the veterinarian: an on-site autopsy provides quick guidance and helps protect the other animals in the group.
Is vaccination enough to solve the problem?
No, but it helps a lot. It reduces the frequency and severity of cases. Without proper ventilation, without limiting density and without spreading constraints around weaning, cases will continue to appear.
Can I reuse the antibiotic that worked last year?
No. The bacteria in question and its sensitivity may be different, and inappropriate treatment wastes the hours that count while promoting resistance. Call your veterinarian, he or she prescribes.
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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