Various respiratory diseases and problems are common. Horses’ airways are sensitive to dust, and sport horses often suffer from respiratory infections. A common symptom of equine respiratory disease is coughing. Coughing is typically caused by diseases and irritations of the lower airways—the trachea, bronchi, and lungs.
Autumn in particular predisposes horses to viral diseases and allergy-related respiratory problems. Viral infections (influenza, herpes, viral arteritis) can, of course, occur year-round. Influenza is often accompanied by other symptoms such as fever. In foals and young horses, the migration of roundworm larvae through lung tissue can cause coughing, and in some cases—especially in trotting racehorses—the cause may be bleeding into the lungs.
Coughing is the airways’ way of clearing themselves and getting rid of harmful factors. A cough can be triggered by many different causes: allergic reactions, increased mucus production, dust particles and other impurities carried into the airways with inhaled air, or breathing very cold or hot air. The release of inflammatory mediators and the shedding of airway surface cells in viral and bacterial infections can also trigger coughing. In many inflammatory airway diseases, sensitivity to coughing increases.¹
Although the underlying purpose of coughing is to clear the airways and remove harmful factors, a strong cough—especially one that persists for a long time—can also be harmful to the horse. Coughing is physically demanding and unpleasant. In severe cases, intense coughing can even reduce oxygen intake.³
The cause of the cough must be identified
The cause is often investigated first through background information: how long the cough has lasted, when or in what situations the horse coughs most, whether there are other symptoms such as fever or nasal discharge, and whether other horses at the yard have similar symptoms. Based on this information alone, it is often possible to determine whether the issue is inflammation or perhaps an airway reaction to irritants.
Examinations often include listening to lung sounds, taking blood samples, endoscopy of the airways, ultrasound of the lungs, or X-rays. In most cases, bloodwork and endoscopy are sufficient for diagnosis.
A cough may be a hypersensitivity reaction
An allergic reaction in the airways leads to mucus production and thickening and constriction of small bronchi. Mucus irritates the airways and causes coughing. If a coughing horse does not have a fever and only one horse in the yard is affected, an allergic cause is often suspected.
RAO (formerly known as “heaves”) is a lung disease in horses that resembles asthma in humans. The most common cause of equine asthma is impurities in inhaled air (e.g., hay dust, mold spores). In horses with asthma, the airways overreact to these irritants and produce more mucus than normal. During an acute asthma attack, the bronchi go into spasm, and over time the airway walls may remodel.⁵
The disease is more common in somewhat older horses. Symptoms include a long-lasting cough, nasal discharge, reduced performance, and labored breathing. As the disease progresses, horses may lose weight. Asthma can cause temporary airway obstruction as inflammatory cells and mucus accumulate in the small bronchi and the airway walls constrict. As in humans, the severity varies—some horses have a milder form and others a more severe one. The underlying mechanism is hypersensitivity to dust and molds.³
Symptoms may initially be occasional coughing in the mornings, at the start of exercise, or while eating or drinking. In more advanced dust allergy, symptoms include coughing, often light-colored nasal discharge, “heaving” or abdominal effort with breathing, and in severe respiratory distress the nostrils may flare. Wheezing and rattling sounds may be heard on exhalation. A typical feature is that symptoms improve when the horse is moved to good stable air or to pasture. Symptoms are usually worse in winter when the horse spends more time indoors and stable doors are kept closed.⁴
Diagnosis is typically based on the characteristic signs, lung auscultation, and lavage samples collected during endoscopy.
Asthma is a chronic disease treated with corticosteroids and bronchodilators. Some horses require low-dose maintenance medication to keep symptoms under control. The disease cannot be cured, but management can often keep the horse symptom-free.³
The most important aspect of asthma management is improving conditions. The horse should be outdoors as much as possible in good air, and stable air quality must be addressed. In the worst cases, a horse may show symptoms after only a few minutes inside the stable. There is also a so-called summer form, where the key is to keep the horse away from dusty paddocks or arenas that trigger symptoms. Sweeping and cleaning the stable should not be done while horses are inside. Hay and bedding should be stored away from stalls. Hay should be offered from the ground. Dry hay is recommended to be soaked to reduce dust; alternatively, the horse should be fed low-dust haylage only. Recommended bedding includes wood shavings, shredded paper, or peat; straw bedding should be avoided.³
Inflammatory airway disease (IAD) resembles heaves in symptoms. The difference is that IAD patients do not typically show labored breathing. Affected horses are often younger than heaves horses. Current understanding suggests that IAD can progress to heaves if the condition is not recognized and treated early. In addition to sensitivity to dust and molds, prolonged bacterial or viral infection or pulmonary hemorrhage may be involved.³
The feared transport pneumonia
The most serious bacterial lower-airway infection in adult horses is so-called transport pneumonia (“shipping fever”). Normal airway clearance requires the horse to keep its head down. Ventilation in transport vehicles may be inadequate, and horses are often tied with their heads up during transport, giving bacteria carried in inhaled air more time to multiply in the lungs.
In addition to coughing and fever, transport pneumonia often causes foul-smelling nasal discharge and breathing difficulties. At its worst, the disease can be life-threatening, and any fever and coughing after transport should be taken seriously.
Rarer causes of coughing include foreign bodies or tumors in the lungs that irritate the airways. Among upper-airway diseases, coughing can be caused by laryngeal problems, the most common being roaring. Various bacterial or fungal infections can also cause coughing, with or without fever.³
When should you seek treatment?
The same principles apply as in humans. A coughing horse can be monitored for a short time if it is otherwise bright and well, and the cough is assumed to be due to a viral infection, for example. If coughing persists for well over a week as the only symptom and affects performance, it is worth at least discussing possible investigations with a veterinarian. If the horse has strong general symptoms such as fever and loss of appetite, you should contact a veterinarian promptly.¹
Stable air quality is essential for respiratory health
Indoor air quality affects the respiratory health and immune resilience of both horses and the people working in the stable. In cold climates, forage and bedding choices matter greatly because horses spend a lot of time indoors. Ventilation must of course be carefully planned when building or renovating, but everyday routines and general cleanliness also influence how many impurities remain in stable air.¹
A horse with asthma should be kept outdoors as much as possible. Even so, good stable air is still crucial. Even if a horse is outside all day (12 hours), it still spends 12 hours inside—which is a long time if it is sensitive to dust indoors. Ideally, the horse would be outside all the time.⁴
Exercise helps loosen mucus, so exercise is allowed unless the horse is in an acute episode of respiratory distress. Vitamin C has been found to have beneficial effects in respiratory issues, so vitamin C supplementation can be tried. Omega-3 fatty acids have anti-inflammatory effects and can be obtained from flax, hemp, and rapeseed oil.⁴
Sources:
1 Rauman Jenni, Koponen Johanna. 2019: Veterinary assessment of reduced performance
2 Hevostietokeskus ry
3 Take a horse’s cough seriously
4 Equine dust hypersensitivity, asthma
5 My horse was diagnosed with asthma – what does it mean?
Read more about the effects of stable air on equine well-being
