Shipping fever is a lower respiratory tract infection seen in horses transported over long distances or experiencing unusual or stressful events. [1]

Known causes of shipping fever include prolonged periods of head elevation, strenuous exercise, anesthesia or complications from a viral illness. [2]

These events increase the amount of debris aspirated by the horse and inhibit the horse’s ability to clear debris from the lungs. Stress also compromises the immune system, making horses susceptible to a viral respiratory infection.

Without prompt medical intervention, shipping fever can develop into pleuropneumonia, which is a dangerous form of equine pneumonia. It is caused by fluid build-up in the lungs and pleural cavity, which is the space between the lungs and chest wall.

Early recognition and treatment of shipping fever are key to a good prognosis. If you are planning on shipping or travelling with your horse, preventative steps can support the immune system and reduce the chance of infection.

Shipping Fever in Horses

Shipping fever is a transport-associated syndrome seen in horses and other livestock animals, causing pyrexia (fever) and other respiratory symptoms. [3]

The stress of travel, combined with exposure to unfamiliar pathogens, can cause various symptoms ranging from mild to severe.

Shipping fever is characterized by the presence of bacteria and other irritants (i.e. hay particles, dust, chemicals) in the lower airway. Longer distances and travel times carry a higher risk of lower airway infection. [3]

Most shipping fever cases present with a general systemic inflammatory response. [4] Signs of infection usually appear within 1-3 days following shipment or arrival at destination and can worsen quickly.

Between 9 – 12% of horses transported for distances between 1,000 – 1,300 km experience shipping fever. [3]

The terms shipping fever and pleuropneumonia are often used interchangeably. However, pleuropneumonia is technically a consequence of severe shipping fever.

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Cause & Pathology

Long-distance travel (or other sudden changes in route) can cause significant stress for the horse, with eleveated levels of the stress hormone cortisol.

High cortisol levels affect the body’s ability to fight off infection, in part by reducing neutrophil counts in the blood. Neutrophils are a type of white blood cell or immune cell that help the body fight infections.

As a result, pulmonary defence mechanisms can become overwhelmed, allowing infection to develop in the lungs. [5] Pneumonia or lung abscesses can develop and extend into the pleural cavity (the fluid-filled space surrounding the lungs). [6]

Shipping fever infection is often polymicrobial or caused by many different bacteria, which may be resistant to certain antibiotics. Infection can worsen quickly, making some cases difficult to treat.

The most common aerobic organisms that cause infection in horses are Streptococcus equi zooepidemicus, Escherichia coli, Actinobacillus and Pasteurella. [4][7]

Common anaerobic organisms include Bacteroides, Clostridium, Peptostreptococcus and Fusobacterium.

Clinical Signs

Before travelling with your horse, ensure that you are able to identify the signs and symptoms of shipping fever. Early detection is important to prevent serious infection.

The following signs indicate shipping fever in the horse: [4][7][8]

  • Nasal discharge
  • Thoracic (chest) pain
  • Elevated body temperature (pyrexia)
  • Cough
  • Rapid, shallow breathing
  • Lethargy
  • Depression
  • Abducted elbows
  • Loss of appetite
  • Reluctance to drink
  • Reluctance to move

Many cases of shipping fever do not present with respiratory signs. Severe pain can inhibit the horse’s ability to cough.

Secondary conditions may develop in advanced cases of shipping fever. These include pulmonary abscessation, colitis and laminitis. [9]

Risk Factors

While any horse can develop shipping fever, competition horses and racehorses have a higher risk due to frequent travel and time spent at high-risk areas (i.e. racetracks and competition grounds). [4][10]

Competition horses are also more likely to come into close contact with horses from different origins, increasing their potential exposure to pathogens. [3]

The horses most affected by shipping are athletic and under five years old. [7]

Transportation & Head Position

Head positioning during transport is considered the most important risk factor for developing shipping fever. [11]

Horses that are cross-tied with their heads raised for extended periods (12-24 hours) may be predisposed to shipping fever. [11]

Cilia are finger-like projections in the trachea, responsible for moving inhaled debris and bacteria away from the lungs. [12]

Prolonged upward fixation of the head allows for the accumulation of bacteria and inflammatory cells in the lower respiratory tract, as the cilia cannot effectively remove debris. Consequently, foreign particles cannot easily move out of the trachea. [12]

Strenuous Exercise

Strenuous exercise can contribute to lower respiratory illness by increasing the rate and depth of aspirated debris. [11] Horses usually develop some lower airway contamination following a bout of exercise.

Intense exercise can also increase the release of the stress hormone cortisol, which impairs the function of pulmonary alveolar macrophages. These immune cells are responsible for finding and removing bacteria and debris from the lungs. [11]

For this reason, strenuous bouts of exercise can reduce the horse’s immune response and increase susceptibility to illness. If a horse is exercised soon after travelling, immune protection of the respiratory tract is further diminished. [11]

Exercise-induced pulmonary hemorrhage (EIPH), commonly seen in Thoroughbred or Standardbred racehorses, creates an ideal environment for bacterial proliferation and infection. [7][13]


Management practices can help to prevent shipping fever in travelling horses by supporting respiratory function and the immune system.

Travel is inherently stressful for horses, which can suppress the immune system. You can reduce your horse’s stress by making several stops when travelling long distances to allow the horse to rest, eat, drink and stretch. [11][15]

Horses shipped over long distances should be allowed to lower their head to the ground several times throughout the trip. [12] Lowering the head and stretching the neck promotes drainage and expulsion of foreign particles from the airways.

Ensure adequate ventilation and minimize dust on the trailer, boat or plane. Poor ventilation can lead to irritation of the respiratory tract and increase the risk of infection.

When transporting your horse, monitor their vital signs so you can quickly detect illness. Elevated body temperature in a travelling horse often indicates shipping fever.

According to the AAEP, a temperature above 101.5oF / 38.6oC is cause for concern. Exercise can also temporarily increase body temperature but it should return to normal within 90 minutes. [16]

Sick or recovering horses should never travel except to receive medical treatment. Their immune system is already weakened, making them susceptible to infection. [12]


All horses that are travelling or being shipped should be vaccinated against common respiratory viruses. Vaccinating horses against influenza can prevent the development of secondary infections, such as shipping fever.

Consult with your veterinarian to learn which vaccines are recommended for your horse. Horses travelling to competitions or racetracks are usually required to be vaccinated for equine herpesvirus 1 and 4 (EHV-1 and EHV-4). [10]


Administering preventative antibiotics to horses before travel is not recommended, as not all cases of pneumonia are bacterial.

Unnecessary use of antibiotics can lead to antibiotic resistance in horses, making it more difficult to treat bacterial illnesses. [12]

Nutritional Immune Support

The best way to support your horse’s immune health is to feed a balanced diet that provides adequate levels of vitamins and minerals and amino acids.

Some of the vitamins and minerals that are essential for the immune system include: [17]

  • Zinc: a trace mineral that is involved in the function of immune signalling molecules known as cytokines.
  • Selenium: an antioxidant trace mineral that is required for immune defence against infection and disease.
  • B-vitamins: help to maintain a healthy nervous system and regulate the body’s stress response.
  • Vitamin E: an important fat-soluble antioxidant that plays a role in immune function

You can ensure that your horse’s nutritional requirements are met by feeding a comprehensive vitamin and mineral supplement, such as Mad Barn’s Omneity.

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Amino acids are also critical for supporting immune function. Besides being components of proteins, several amino acids (particularly arginine and glutamine ) have important roles in the function of immune cells. [18] Consult with an equine nutritionist to ensure protein and amino acid supply is adequate in your horse’s diet.

Respiratory Support

Some nutritional supplements have been studied for their effects on respiratory health in horses. These supplements may not prevent shipping fever when transporting a horse, but they can support the horse’s lung function to reduce the risk of respiratory issues.

Spirulina is a blue-green algae that is a rich source of vitamins, antioxidants, proteins, fatty acids and minerals. It has been shown to support respiratory function in horses due to its anti-inflammatory and antihistamine properties.

It has been reported that spirulina reduced respiratory symptoms, including coughing, sneezing and headshaking in horses with recurrent respiratory issues. The horses also had better exercise performance, improved race times, and better respiratory recovery after moderate exercise. [20]


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Mad Barn’s W-3 Oil is fat supplement that contains high levels of the omega-3 fatty acid DHA and Vitamin E.

Omega-3’s are polyunsaturated fatty acids that are recognized for their health-boosting effects in horses. In addition to supporting immune function and normal stress responses, they also help maintain respiratory health.

In one study, two months of DHA supplementation improved clinical scores of respiratory dysfunction by 60%. This resulted in less coughing and inflammation, as well as improved lung function in horses with recurrent breathing issues. [21]

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Gut Health

Horses travelling to competition are also at high risk of gastric ulcers and other gut issues. [19]

When horses are trailered, they often experience stress, changes to their normal feeding routine, reduced access to forage and water, and changes to their environment and social grouping. All of these are risk factors for the development of gastric ulcers.

Ulcers can further compromise the immune system as toxins and pathogens are able to penetrate the gastrointestinal barrier, triggering inflammation and an immune response.

Mad Barn’s Visceral+ is a pelleted gut health supplement recommended by veterinarians for horses travelling to the competition. Visceral+ is formulated to maintain gastric and hindgut health and support the horse’s immune system.


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Shipping fever can be diagnosed based on health history, clinical signs and diagnostic testing. Horses that have travelled long distances, whether by air, sea, rail or road, should be carefully monitored for several days following arrival at their destination.

Rectal temperatures should be taken twice a day for three days. If a fever is present, contact a veterinarian immediately. [8]

The veterinarian will ask for the horse’s travel history and then examine the horse for nasal discharge, foul-smelling breath, chest pain and coughing. These are signs of bacterial infection of the lungs.

Differential Diagnosis

The clinical signs of shipping fever can be confused with other respiratory infections or conditions such as colic, laminitis or exertional rhabdomyolysis. [4] A veterinarian will conduct a full clinical examination of the body to rule out abdominal pain that can be indicative of other conditions.


Blood may be collected from horses with suspected shipping fever for hematological evaluation.

If the horse has an acute infection, the following clinicopathological abnormalities can be expected on the blood test: [4][13]

  • Increased neutrophil count (leukocytosis)
  • Elevated serum amyloid A (SAA)
  • Elevated fibrinogen (hyperfibrinogenemia)
  • Mild to moderate decrease in packed cell volume (PCV)
  • Increased total plasma protein

Rarely is a diagnosis of shipping fever made based on blood test results. Early intervention is crucial, and waiting for results before treatment is not feasible.

However, bloodwork may be warranted before travelling with your horse to look for signs of inflammation or infection. [12]

Ultrasonography & Radiography

These diagnostic imaging techniques can provide important information about your horse’s pleura and pleural cavity and identify any abnormalities. [4][13]

Ultrasonography can assess the character of the fluid in the lungs (including the presence of gas echoes). Ultrasound can also examine the surface of the lungs and identify abscesses.

Radiography can be used to detect disease or deep abscesses in the interstitial lining of the lung. These deep lesions cannot be identified with ultrasound. [4]

Thoracocentesis (Pleurocentesis)

Horses with shipping fever often have a build-up of fluid around the lungs, otherwise known as pleural effusion.

In order to diagnose shipping fever and slowly drain excess fluid from the pleural space, a minimally invasive and relatively inexpensive procedure called thoracocentesis is conducted.

Following an ultrasound to locate the appropriate site, an incision is made through the skin and intercostal muscle. A chest tube is placed into the pleural space to obtain a fluid sample for diagnosis or to drain the fluid for treatment. [22]

In some cases of shipping fever, bilateral thoracentesis is needed to remove fluid around both of the horse’s lungs.


A respiratory tract endoscopy is a diagnostic procedure in which an endoscope – a thin, flexible tube with a camera at the end – is passed into the respiratory tract for visual inspection.

Endoscopy is often performed to allow the clinician to examine the condition of the airways and identify different pathogens that could be causing the infection. [4] A fluid sample can be retrieved through endoscopy and submitted for laboratory analysis.

This diagnostic method allows the clinician to determine whether aerobic or anaerobic bacteria (or a mixture of both) are causing infection. A treatment plan can then be tailored to the individual horse.


Early treatment is essential when it comes to shipping fever in horses. [12] Rapid resolution is possible if treatment begins within 48 hours of the initial onset of infection.

However, anaerobic bacteria can multiply quickly, leading to severe infection and worsening symptoms. If treatment begins after 48 hours, a poor response can be expected.

Shipping fever-affected horses may develop sepsis due to severe bacterial infection. This is a medical emergency, and aggressive treatment is needed. [2]

Antimicrobial Drugs

Antimicrobials are administered to combat the wide spectrum of microorganisms that cause shipping fever. [4] Gram-positive or most other anaerobic bacteria are treated with a wide-range antibiotic, such as penicillin.

Penicillin and other antibiotics may be paired with an aminoglycoside (gentamicin) to treat shipping fever caused by drug-resistant or gram-negative bacteria. [13]

Anti-inflammatory drugs

Non-steroidal anti-inflammatories (NSAIDs) or opioids may be administered to affected horses for pain relief.

Modulating the inflammatory response through analgesics can stimulate the horse’s appetite and enable them to move around, which is important for recovery. [13] NSAIDs can also help reduce or control a fever.

NSAIDs that are commonly used to treat shipping fever include flunixin, meglumine or phenylbutazone. [4]

Supportive care

Horses with shipping fever often develop hypovolaemia or low extracellular fluid volume. [4] This may be caused by poor hydration or the build-up of fluid in the lining of the lungs and chest cavity. Affected horses may need IV fluids to prevent dehydration and weakness.

Daily ultrasound exams allow clinicians to monitor fluid build-up, drainage and infection in the recovering horse. [7]


The survival rate for horses with shipping fever is between 43 – 76%, although some reports suggest it could be as high as 90%. [4][7] The prognosis for horses with shipping fever has improved significantly over the past two decades.

Between 50 – 60% of the horses that survive the disease return to their previous level of work. Others become breeding, trail or lesson horses. [11] If the infection is caught early, horses can recover fully.

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  1. Oikawa, M. et al. Some Aspects of the Stress Responses to Road Transport in Thoroughbred Horses with Special Referene to Shipping Fever. J EquineSci.2004.
  2. Arroyo, M. G. et al. Factors Associated with Survival in 97 Horses with Septic Pleuropneumonia. J Vet Intern Med. 2017. View Summary
  3. Maeda, Y. Oikawa, M. Patterns of Rectal Temperature and Shipping Fever Incidence in Horses Transported Over Long-Distances. Front. Vet. Sci. 2019.View Summary
  4. Copas, V. Diagnosis and treatment of equine pleuropneumonia. In Practice. 2011.
  5. Dechant, J. Combination of medical and surgical therapy for pleuropneumonia in a horse. Can Vet J. 1997. View Summary
  6. Hudson, N. P. H. et al. Case of pleuropneumonia with complications in a Thoroughbred stallion. Equine Vet Educ.1999.
  7. Rush, B. R. Pleuropneumonia in Horses. Merck Manual Veterinary Manual. 2014.
  8. Leadon, D. et al. Veterinary management of horse transport. Vet Ital. 2008. View Summary
  9. Hurley, M. J. et al. The incidence and risk factors for shipping fever in horses transported by air to Hong Kong: Results froma2-yearprospective study. Vet J. 2016.View Summary
  10. AAEP Infectious Disease Committee. Equine Herpesvirus (EHV). American Association of Equine Practitioners. 2021.
  11. Racklyeft, D. J. et al. Towards an understanding of equine pleuropneumonia: factors relevant for control. Aust Vet J. 2000. View Summary
  12. Norton, J. Preventing Shipping Fever. American Association of Equine Practitioners. 2016.
  13. Raidal, S. L. Equine Pleuropneumonia. Br vet J. 1995. View Summary
  14. Brown-Douglas, C. Feeding Horses Before Travel. Kentucky Equine Research. 2011.
  15. Espy, B. How Do I Take My Horse’s Temperature?. AAEP. 2016.
  16. Childs, C.E. et al. Diet and Immune Function. Nutrients. 2019.
  17. Grohmann, U. and Bronte, V. Control of immune response by amino acid metabolism. Immunol Rev. 2010.
  18. Padalino, B. et al. Effects of transportation on gastric pH and gastric ulceration in mares. J Vet Intern Med. 2020. View Summary
  19. Kellon, Eleanor Use of the Herb Gynostemma Pentaphyllum and the Blue-green Algae Spirulina Platensis in Horses. Equine Congress. 2006.
  20. Nogradi, N. et al. Omega-3 Fatty Acid Supplementation Provides an Additional Benefit to a Low-Dust Diet in the Management of Horses with Chronic LowerAirwayInflammatory Disease. J Vet Intern Med. 2015.
  21. Chaffin, M. K. Thoracocentesis and pleural drainage in horses. Equine vet Educ. 1998.