Pneumonia in Horses and Foals: Rhodococcus, Shipping Fever, and Emergency Signs
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Pneumonia in Horses and Foals: Rhodococcus, Shipping Fever, and Emergency Signs
By Dr Duncan Houston
Pneumonia in horses is not something to casually monitor from the paddock for a few days.
A mild cough after dusty hay is one thing. A horse with fever, dullness, rapid breathing, nasal discharge, reduced appetite, pain around the chest, or a foal that seems quieter than normal is a very different situation.
There are two important problems owners often mix together. Adult horses can develop bacterial pneumonia or pleuropneumonia, often after long distance transport, viral respiratory infection, choke, general anaesthesia, or another stressor that compromises lung defence. Foals can develop pneumonia from several causes, but Rhodococcus equi is one of the most serious, especially in young foals on endemic breeding farms. (Merck Veterinary Manual)
The clinical trap is that early signs can be subtle. A foal with Rhodococcus may only look mildly dull or have a fever before advanced lung abscesses are obvious. An adult horse after transport may look “a bit off” before pleuropneumonia becomes painful, expensive, and potentially life threatening.
Quick Answer
Pneumonia in adult horses is often linked to transport, viral respiratory disease, choke, anaesthesia, or aspiration, while Rhodococcus equi pneumonia is mainly a disease of foals around 1 to 5 months of age. Warning signs include fever, cough, lethargy, increased breathing rate, laboured breathing, reduced appetite, nasal discharge, and pain or reluctance to move. Foals with suspected Rhodococcus, and any horse with fever plus breathing difficulty, recent long distance transport, or chest pain, need prompt veterinary assessment. (Merck Veterinary Manual)
What Is Pneumonia in Horses?
Pneumonia means infection and inflammation involving the lungs and lower airways.
In horses, pneumonia is concerning because the lungs are large, the disease can progress into deeper lung tissue, and infection can spread into the pleural space around the lungs. When that happens, it becomes pleuropneumonia, sometimes called shipping fever when linked with transport.
A simple way to think about it:
| Condition | What it means | Why it matters |
|---|---|---|
| Bronchopneumonia | Infection involving the bronchi and lung tissue | Can cause fever, cough, dullness, and breathing changes |
| Pleuropneumonia | Pneumonia that extends to the pleura and chest cavity | More painful and often more serious |
| Rhodococcus pneumonia | A foal pneumonia caused by Rhodococcus equi | Can cause lung abscesses and can be difficult to detect early |
| Aspiration pneumonia | Pneumonia after inhaling feed, saliva, fluid, or material into the lungs | Often linked with choke or swallowing problems |
| Shipping fever | Pleuropneumonia associated with transport stress and elevated head position | Can appear within days after travel |
The real concern is not just that the horse has a cough. The concern is whether infection has reached the lower airways, whether the horse is oxygenating properly, and whether the disease is progressing toward abscesses or pleuropneumonia.
Adult Horse Pneumonia vs Rhodococcus in Foals
This distinction matters.
Rhodococcus equi pneumonia is primarily a foal disease. Adult horses can develop pneumonia, but adult bacterial pneumonia is usually not Rhodococcus unless the horse is immunocompromised or there is an unusual circumstance. Merck describes Rhodococcus equi as the most common and serious cause of pneumonia in foals 1 to 5 months old, with clinical disease rare in horses older than 8 months. UC Davis describes it as a soil associated bacterium that causes pneumonia mainly in foals 1 to 6 months old. (Merck Veterinary Manual)
| Patient | More likely causes |
|---|---|
| Young foal | Rhodococcus equi, other bacterial pneumonia, viral disease, sepsis, aspiration, environmental stress |
| Adult horse after travel | Bacterial pneumonia or pleuropneumonia, often linked with transport stress and elevated head carriage |
| Adult horse after choke | Aspiration pneumonia |
| Adult horse after viral infection | Secondary bacterial pneumonia |
| Adult horse after anaesthesia | Reduced airway defence, aspiration risk, secondary pneumonia |
| Immunocompromised adult horse | Unusual infections become more possible |
The mistake is treating “horse pneumonia” as one disease. Age, history, transport, farm risk, and clinical pattern change the most likely diagnosis.
What Is Rhodococcus equi?
Rhodococcus equi is a gram positive, facultative intracellular bacterium that lives in soil and manure. Pathogenic strains contain the VapA virulence factor, which helps the bacterium survive inside macrophages. Foals are most commonly infected early in life, and disease may progress slowly before obvious signs develop.
Rhodococcus is especially important on endemic breeding farms, where the organism becomes established in the environment and cases may appear in foal crops year after year.
The classic disease is a subacute to chronic bronchopneumonia with abscess formation in the lungs. Some foals also develop problems outside the lungs, including abdominal abscesses, enterocolitis, joint disease, bone infection, uveitis, pericarditis, or other less common sites. (Merck Veterinary Manual)
Why Rhodococcus Can Be Missed Early
Rhodococcus pneumonia can be frustrating because early signs are often mild.
A foal may still nurse. They may still move around. The cough may be occasional or absent. Nasal discharge may not be obvious. The first clues can be fever, mild dullness, increased breathing rate, or subtle reduced energy.
Merck notes that clinical signs are difficult to detect until lung infection reaches a critical point, and early signs may include lethargy, fever, occasional cough, and slight rapid breathing that may not be obvious at rest. (Merck Veterinary Manual)
In practice, this is why foal monitoring matters. The foal that is “just quieter today” can sometimes be the one that needs a temperature check and veterinary assessment.
Signs of Pneumonia in Adult Horses
Adult horses with pneumonia or pleuropneumonia may show:
| Sign | Why it matters |
|---|---|
| Fever | Common sign of infection or inflammation |
| Dullness or depression | The horse may be systemically unwell |
| Reduced appetite | Often appears early in significant illness |
| Cough | May be present, but absence of cough does not rule pneumonia out |
| Nasal discharge | Can occur with respiratory infection |
| Rapid breathing | Lower airway or lung involvement |
| Laboured breathing | More serious respiratory compromise |
| Increased heart rate | Pain, fever, dehydration, or systemic inflammation |
| Reluctance to move | Can occur with pleural pain |
| Pain over the ribs or chest | Suggests pleuropneumonia or pleuritis |
| Weight loss | More common with longer standing disease |
Merck describes early pleuropneumonia signs as fever, tachycardia, depression, lethargy, inappetence, and sometimes mild colic, with respiratory distress and chest pain signs becoming more obvious as disease progresses. (Merck Veterinary Manual)
Signs of Rhodococcus Pneumonia in Foals
Foals with Rhodococcus pneumonia may show:
| Sign | Why it matters |
|---|---|
| Fever | Often one of the earliest clues |
| Dullness or lethargy | May be subtle |
| Increased breathing rate | Important early respiratory clue |
| Laboured breathing | More advanced disease |
| Cough | Can occur, but may not be reliable |
| Poor growth | Chronic disease may affect development |
| Reduced nursing or appetite | More concerning in young foals |
| Nasal discharge | Less common than many owners expect |
| Wheezes or crackles | Found on veterinary auscultation |
| Abdominal signs | Possible extrapulmonary disease |
| Lameness or swollen joints | Possible joint or bone involvement |
AAEP guidelines note that early Rhodococcus signs in foals may include fever, lethargy, and anorexia, and that cough and nasal discharge are unreliable signs.
Why Long Distance Transport Can Trigger Pneumonia
Shipping fever is not just “stress from travel”.
During transport, horses are often tied with their heads elevated. This interferes with the normal ability to lower the head, drain airway secretions, and clear inhaled bacteria and debris. Transport stress also affects immune function. Merck states that long distance transport, especially with the head restrained in an elevated position, is the most common risk factor for pleuropneumonia, and bacterial colonisation of the lower airway can occur within 12 to 24 hours under these conditions. (Merck Veterinary Manual)
Risk increases with:
| Transport factor | Why it matters |
|---|---|
| Long travel duration | More time with impaired airway clearance |
| Head tied high | Reduces natural drainage |
| Poor ventilation | Increases dust and airborne irritants |
| Hay nets at head height | Increases inhaled particles |
| Dehydration | Thickens secretions |
| Stress and fatigue | Reduces immune defence |
| No rest breaks | Less opportunity to recover and lower the head |
| Travel after viral illness | Compromised airways are more vulnerable |
A horse that develops fever, cough, dullness, or fast breathing within a week of transport deserves a veterinary check, even if the signs look mild.
What Is Pleuropneumonia?
Pleuropneumonia is a severe form of pneumonia where infection and inflammation extend into the pleura and pleural space around the lungs. This can cause painful fluid accumulation in the chest and can make breathing more difficult.
The more specific signs often relate to pain. Horses may stand braced, avoid turning, resist lying down, grunt when pressure is applied over the ribs, or appear anxious and uncomfortable. These signs can sometimes be mistaken for colic. (Merck Veterinary Manual)
Pleuropneumonia is not a “give antibiotics and hope” situation. It may require ultrasound, tracheal wash, pleural fluid sampling, culture, broad spectrum antimicrobials, pain control, drainage with chest tubes, and sometimes surgery in severe or unresponsive cases. (Merck Veterinary Manual)
How Worried Should You Be?
| Risk level | What it looks like | What it may mean | What to do |
|---|---|---|---|
| Low concern | Occasional cough, bright horse, normal temperature, normal breathing, no travel or outbreak risk | Mild irritation, dust, allergy, early viral signs | Monitor closely and check temperature |
| Moderate concern | Fever, mild cough, dullness, nasal discharge, or recent travel but normal breathing effort | Viral infection, early bacterial pneumonia, early transport related disease | Call your vet and arrange assessment |
| High concern | Fever plus rapid breathing, laboured breathing, poor appetite, depression, foal under 6 months, or recent long distance transport | Pneumonia or early pleuropneumonia | Veterinary assessment is needed promptly |
| Critical | Severe breathing effort, flared nostrils, blue or grey gums, chest pain, reluctance to move, collapse, severe fever, foal struggling to breathe, or suspected pleuropneumonia | Respiratory emergency | Call your vet urgently |
The decision checkpoint is simple: fever plus breathing changes is not a wait and see problem.
What Else Can Look Like Pneumonia?
Coughing and nasal discharge do not automatically mean pneumonia.
Important rule outs include:
| Condition | Why it can look similar |
|---|---|
| Equine influenza | Fever, cough, nasal discharge, rapid spread |
| Equine herpesvirus respiratory disease | Fever, respiratory signs, outbreak concern |
| Strangles | Fever, nasal discharge, lymph node swelling |
| Equine asthma | Cough and breathing effort, often no fever |
| Dust or mould irritation | Coughing, nasal irritation |
| Choke | Nasal discharge with feed material, aspiration risk |
| Pleuropneumonia | Pneumonia with chest cavity involvement |
| Lung abscess | Chronic fever, weight loss, respiratory signs |
| Exercise induced pulmonary haemorrhage | Blood from nostrils or poor performance |
| Heart disease | Exercise intolerance, breathing difficulty |
| Foal sepsis | Fever, dullness, respiratory signs in very young foals |
| Parasite migration in foals | Respiratory signs in young horses |
The real clinical question is not “is there a cough?” It is: is the horse systemically unwell, is there fever, and is the lower respiratory tract involved?
How Do Vets Diagnose Pneumonia in Horses?
A proper pneumonia workup is usually structured around the horse’s age, history, signs, and severity.
Common diagnostic steps include:
| Diagnostic step | Why it matters |
|---|---|
| Temperature, heart rate, respiratory rate | Establishes severity |
| Lung auscultation | Detects wheezes, crackles, dull areas, or reduced sounds |
| Rebreathing exam | Helps reveal lower airway sounds in adult horses |
| Bloodwork | Assesses infection, inflammation, dehydration, and systemic effects |
| Thoracic ultrasound | Detects pleural fluid, consolidation, abscesses, and chest wall involvement |
| Thoracic radiographs | Useful for deeper lung lesions and abscesses |
| Tracheal wash | Allows cytology, culture, PCR, and sensitivity testing |
| Pleurocentesis | Samples pleural fluid in suspected pleuropneumonia |
| Culture and sensitivity | Guides antimicrobial choice |
| Viral testing | Important in outbreaks or suspected influenza or herpesvirus |
For adult bacterial pneumonia, tracheal aspirates, bloodwork, and ultrasound are commonly used to guide diagnosis and treatment decisions. NC State’s equine pneumonia research page also notes that bacterial pneumonia commonly develops after long distance transport, viral infection, or choke, and that cultures of tracheal aspirates are performed at diagnosis in their treatment study. (College of Veterinary Medicine)
How Is Rhodococcus Diagnosed in Foals?
Rhodococcus diagnosis is more specific than simply seeing a foal with pneumonia.
A definitive diagnosis relies on collecting a sterile lower airway sample, usually by tracheal wash, then performing bacterial culture, cytology, and PCR testing for the VapA gene where possible. AAEP guidelines specifically note that VapA PCR can support diagnosis but should not replace bacterial culture, because PCR does not confirm live organisms or provide antimicrobial susceptibility results.
Veterinarians may also use:
| Test | Why it helps |
|---|---|
| Thoracic ultrasound | Finds peripheral lung abscesses and consolidation |
| Thoracic radiographs | Detects deeper lung lesions |
| Bloodwork | Assesses inflammation, white cell changes, fibrinogen, and systemic status |
| Tracheal wash culture | Confirms bacteria and guides antibiotic choice |
| VapA PCR | Supports identification of virulent Rhodococcus |
| Abdominal ultrasound | Looks for extrapulmonary disease when signs suggest it |
| Joint fluid sampling | Used if lameness or joint swelling suggests septic arthritis |
On endemic farms, ultrasound can support a presumptive diagnosis, but treating clinically normal foals based only on small ultrasound lesions is not recommended because it can contribute to antimicrobial resistance.
How Is Pneumonia Treated in Adult Horses?
Treatment depends on severity, cause, culture results, and whether pleuropneumonia is present.
A treatment plan may include:
| Treatment | Why it may be used |
|---|---|
| Antimicrobials | Treat bacterial infection |
| NSAIDs | Reduce fever, pain, and inflammation |
| Fluids | Support hydration in systemically unwell horses |
| Rest | Allows recovery and reduces respiratory stress |
| Nutrition support | Maintains strength during illness |
| Thoracic drainage | Needed in many pleuropneumonia cases |
| Oxygen support | Used in severe respiratory compromise |
| Repeated monitoring | Tracks response and complications |
Pleuropneumonia often needs longer and more aggressive treatment than uncomplicated pneumonia. Merck states that treatment typically requires long term broad spectrum antimicrobials and drainage of pleural fluid using indwelling chest tubes, with thoracotomy useful in some long standing cases that do not respond to standard treatment. (Merck Veterinary Manual)
The important clinical point: antibiotics should be selected and adjusted by a vet, ideally using culture and sensitivity when possible.
How Is Rhodococcus Pneumonia Treated in Foals?
Foals with confirmed severe Rhodococcus pneumonia are commonly treated with a macrolide antibiotic combined with rifampin. Clarithromycin and azithromycin are often preferred over erythromycin because of better bioavailability, and treatment duration depends on severity and response. (Merck Veterinary Manual)
Treatment may include:
| Treatment area | Why it matters |
|---|---|
| Macrolide plus rifampin | Standard treatment for confirmed severe disease |
| Culture and sensitivity | Important because resistance can occur |
| NSAIDs | Helps control fever and inflammation |
| Hydration support | Supports sick foals |
| Oxygen | Needed in severe respiratory compromise |
| Cool, ventilated environment | Important because macrolides can contribute to hyperthermia |
| Monitoring ultrasound or radiographs | Tracks lesion resolution |
| Monitoring for side effects | Diarrhoea, overheating, tachypnoea, and dam colitis risk matter |
Macrolide and rifampin treatment is not harmless. Reported adverse reactions include diarrhoea, hyperthermia, tachypnoea, and potentially serious antimicrobial associated enterocolitis in dams exposed to macrolides. (Merck Veterinary Manual)
This is why Rhodococcus treatment should be targeted, monitored, and not started casually just because an ultrasound found a tiny lesion in a clinically normal foal.
Why Antibiotic Resistance Matters
Rhodococcus equi resistance is a major concern on endemic farms.
Widespread treatment of subclinical foals has been linked with the emergence of macrolide and rifampin resistant strains. AAEP guidelines state that treatment of clinically normal foals with small pulmonary lesions is often unnecessary and does not accelerate lesion resolution, and that many foals with small numbers of abscesses can resolve spontaneously without treatment.
The mistake is thinking more antibiotics always means better prevention. With Rhodococcus, overuse can make the farm problem harder for future foals.
When Is This an Emergency?
Call your vet urgently if you see any of these signs:
| Red flag | Why it matters |
|---|---|
| Fever plus rapid breathing | Strong concern for lower respiratory disease |
| Laboured breathing | Possible respiratory compromise |
| Flared nostrils or abdominal effort | More serious breathing difficulty |
| Blue, purple, or grey gums | Oxygenation concern |
| Foal under 6 months with fever or dullness | Rhodococcus or other foal pneumonia must be considered |
| Horse recently transported and now feverish or dull | Shipping fever or pleuropneumonia risk |
| Chest pain or reluctance to move | Possible pleuropneumonia |
| Persistent fever despite treatment | Infection may be progressing or treatment may be wrong |
| Reduced appetite with respiratory signs | Systemic illness |
| Collapse or severe weakness | Emergency |
| Choke followed by cough, fever, or nasal discharge | Aspiration pneumonia risk |
| Nasal discharge with feed material | Choke or aspiration concern |
A horse that is breathing hard is not a horse to watch overnight.
What Should You Do Right Now?
1. Take the temperature
A rectal temperature is one of the most useful first checks. Fever changes the urgency.
2. Count the respiratory rate
Count breaths at rest. Fast breathing, especially with effort, is more concerning than a mild occasional cough.
3. Look at breathing effort
Watch the nostrils, abdomen, chest, and posture. Laboured breathing needs urgent attention.
4. Isolate if infection is possible
If viral respiratory disease is possible, reduce contact with other horses until your vet advises.
5. Do not exercise the horse
Rest is important when pneumonia, viral disease, or fever is suspected.
6. Do not start leftover antibiotics
The wrong antibiotic can delay proper treatment and interfere with culture results.
7. Call your vet promptly
Mention age, fever, breathing rate, recent transport, choke, viral exposure, foal farm history, vaccination status, and whether other horses are sick.
8. Keep foals low stress
Handling and stress can worsen respiratory effort in foals with Rhodococcus or other pneumonia.
9. Improve air quality
Reduce dust, avoid dusty hay, improve ventilation, and move sick horses away from heavy dust or ammonia.
10. Track changes
Record temperature, breathing rate, appetite, cough frequency, nasal discharge, medications, and behaviour.
How Can Pneumonia Be Prevented?
You cannot prevent every pneumonia case, but you can reduce risk.
Adult horse prevention
| Prevention step | Why it helps |
|---|---|
| Vaccinate appropriately for influenza and EHV | Reduces viral respiratory disease risk |
| Avoid travel when sick or recently exposed | Reduces pneumonia and outbreak risk |
| Allow head lowering during transport where safe | Supports airway clearance |
| Use rest breaks on long trips | Reduces transport stress |
| Improve trailer ventilation | Reduces dust and airborne irritants |
| Avoid dusty hay nets at head height | Reduces inhaled particles |
| Manage choke promptly | Reduces aspiration risk |
| Monitor after anaesthesia | Early detection of respiratory complications |
| Check temperature after long travel | Finds early shipping fever signs |
| Quarantine new arrivals | Reduces viral spread |
Viral respiratory infections, transport, anaesthesia, and dysphagia or choke can impair normal lower airway defences and increase pneumonia risk in adult horses. (IVIS)
Rhodococcus prevention in foals
There is no fully effective vaccine for Rhodococcus. On endemic farms, control relies on foal monitoring, early detection, reducing severe clinical disease, and in some cases, Rhodococcus specific hyperimmune plasma. AAEP guidelines state that absolute prevention is unlikely, and that the main goal is reducing clinical pneumonia while limiting unnecessary antibiotic use.
Useful prevention strategies include:
| Prevention step | Why it helps |
|---|---|
| Identify endemic farms | Farm history changes risk |
| Monitor foals closely from early life | Early signs are subtle |
| Temperature checks in high risk foals | Fever may be an early clue |
| Thoracic ultrasound screening where appropriate | Useful on endemic farms |
| Avoid treating clinically normal foals solely for small lesions | Helps reduce antimicrobial resistance |
| Manage dust | Reduces inhalation exposure |
| Reduce overcrowding | Lowers environmental and stress pressure |
| Good ventilation | Supports respiratory health |
| Hyperimmune plasma on endemic farms when advised | May reduce clinical pneumonia risk |
| Veterinary farm plan | Each endemic farm needs a tailored protocol |
Rhodococcus control is a farm level problem, not just a single foal treatment decision.
Is Rhodococcus Contagious?
Rhodococcus is not usually managed like influenza, where one coughing horse directly infects the next and the whole yard needs classic respiratory isolation.
The bigger issue is environmental contamination. Foals with pneumonia shed higher numbers of Rhodococcus in faeces, which can contaminate the environment. AAEP notes there is no evidence that Rhodococcus infection is contagious among foals in the usual direct sense, and that exposure to virulent Rhodococcus is widespread in foal environments.
There is also zoonotic potential, mainly for immunosuppressed people. UC Davis and AAEP both note that Rhodococcus can infect immunocompromised humans, although disease in healthy people is rare. (ceh.vetmed.ucdavis.edu)
Practical approach: use good hygiene, manage manure and dust, and be extra careful around immunocompromised handlers.
Common Mistakes Owners Make
Mistake 1: Waiting because the cough is mild
A cough can be mild while lower airway disease is developing. Fever and breathing rate matter more than cough alone.
Mistake 2: Missing fever in foals
Foals with Rhodococcus can look only slightly dull early. Temperature checks are essential on high risk farms.
Mistake 3: Treating all ultrasound lesions with antibiotics
On endemic farms, clinically normal foals with small lesions may clear disease without treatment, and unnecessary treatment can contribute to resistance.
Mistake 4: Using leftover antibiotics
Pneumonia treatment should be based on likely organisms, severity, culture results, and the individual horse. Guessing can cause harm.
Mistake 5: Ignoring transport history
Fever or dullness after long distance travel should raise suspicion for shipping fever or pleuropneumonia.
Mistake 6: Not checking after choke
Aspiration pneumonia can develop after choke, even when the initial obstruction seems resolved.
Mistake 7: Exercising too soon
Respiratory recovery takes time. Returning too early can delay recovery and worsen stress.
Mistake 8: Confusing asthma with pneumonia
Equine asthma can cause cough and breathing effort, but fever, dullness, and systemic illness point more toward infection.
Will My Horse or Foal Be Okay?
Many horses and foals recover well when pneumonia is diagnosed early and treated appropriately.
The outlook is better when:
| Good sign | Why it helps |
|---|---|
| Treatment starts early | Less lung damage and lower complication risk |
| Breathing effort is mild | Lower immediate risk |
| Horse remains bright and eating | Better systemic stability |
| Culture guides antibiotics | More targeted treatment |
| No pleural fluid | Less severe than pleuropneumonia |
| No abscesses | Simpler recovery |
| Foal has uncomplicated pulmonary Rhodococcus | Better prognosis than extrapulmonary disease |
| Response is seen within days | Suggests treatment is working |
| Rechecks are performed | Catches relapse or complications early |
The outlook becomes more guarded when there is severe respiratory distress, pleuropneumonia, chest fluid, anaerobic infection, lung abscesses, extrapulmonary Rhodococcus, abdominal abscesses, septic joints, poor response to antibiotics, or delayed treatment. Merck reports that survival for Rhodococcus pneumonia with appropriate treatment is around 60 to 90 percent depending on severity, while survival in pleuropneumonia varies widely with disease severity and how long signs were present before appropriate treatment began. (Merck Veterinary Manual)
Related Horse Health Topics To Link Internally
| Related topic | Why it connects |
|---|---|
| Fever in Horses | Fever is often the first clue in pneumonia |
| Coughing in Horses | Cough can be mild or serious depending on context |
| Shipping Fever in Horses | Long distance transport is a major risk factor |
| Choke in Horses | Aspiration pneumonia can follow choke |
| Foal Fever | Young foals need faster assessment |
| Equine Influenza | Viral disease can predispose to bacterial pneumonia |
| Pleuropneumonia in Horses | Severe pneumonia with chest cavity involvement |
FAQs About Pneumonia and Rhodococcus in Horses
Is Rhodococcus pneumonia mainly a foal disease?
Yes. Rhodococcus equi pneumonia primarily affects foals around 1 to 5 or 6 months of age. Clinical disease is rare in older horses unless they are immunocompromised or in unusual circumstances. (Merck Veterinary Manual)
Can adult horses get pneumonia after transport?
Yes. Long distance transport, especially when the horse’s head is restrained high, is a major risk factor for pleuropneumonia. Signs often appear within days after travel and can include fever, dullness, rapid breathing, cough, and chest discomfort. (Merck Veterinary Manual)
Does every foal with small lung lesions need antibiotics?
No. On endemic farms, some clinically normal foals with small pulmonary lesions can clear infection without treatment. Treating every subclinical lesion can contribute to macrolide and rifampin resistance, so treatment decisions should be made with a vet using the full clinical picture.
How is Rhodococcus confirmed?
Definitive diagnosis usually requires a lower airway sample, such as a tracheal wash, submitted for bacterial culture, cytology, and VapA PCR where available. Ultrasound or radiographs can support the diagnosis, especially on endemic farms.
When should I call the vet for a coughing horse?
Call your vet if there is fever, rapid breathing, laboured breathing, reduced appetite, dullness, nasal discharge, recent long distance transport, recent choke, or if the horse is a foal under 6 months with fever or lethargy.
The Bottom Line
Pneumonia in horses is not one single disease.
In adult horses, the most important risks include transport, viral respiratory disease, choke, anaesthesia, aspiration, and progression to pleuropneumonia. In foals, Rhodococcus equi is one of the most serious causes of pneumonia, especially on endemic breeding farms, and it can be easy to miss early.
The safest rule is simple: fever plus breathing changes needs veterinary attention. A foal with fever or dullness, or any horse that becomes unwell after long distance travel or choke, should not be monitored casually.
Early diagnosis gives you the best chance of choosing the right treatment, protecting the lungs, reducing complications, and avoiding unnecessary antibiotics where they are not needed.
If you are unsure whether your horse’s cough, fever, breathing changes, travel history, or foal pneumonia signs are urgent, ASK A VET™ can help you understand what signs matter and when veterinary care is needed.