Equine COPD – or chronic obstructive pulmonary disease – is a now-obsolete term for a common condition in horses that causes coughing and poor performance.

This condition is now referred to as equine asthma and is one of the most common non-infectious lung diseases. Severe equine asthma affects 14–17% of horses in some populations, but up to 70% of pleasure horses have indicators of mild to moderate asthma. [5]

Horses affected by equine asthma typically have increased mucus production, difficulty breathing during exercise and sometimes at rest, cough, and nasal discharge. More severe cases may result in acute respiratory distress.

Equine COPD is thought to have various triggers, including fungal spores, bacterial endotoxins, inorganic dust material, and storage mites. [2]

The key to success in treating horses with COPD is a combination of strict environmental management and feeding practices with medications as needed for respiratory distress or flare-ups.

Equine COPD

Chronic obstructive pulmonary disease has been diagnosed and researched in horses since the 1970s, but this term is now outdated.

Recently the American College of Veterinary Internal Medicine (ACVIM) updated a consensus statement about equine inflammatory airway disease.

Equine asthma (EA) is the accepted umbrella term incorporating non-infectious, inflammatory airway disease, including heaves, COPD, inflammatory airway disease (IAD), recurrent airway obstruction (RAO), and “broken wind”. [1]

However, many horse owners still use the terms COPD and RAO when referring to their horses with respiratory issues. For this reason, we sometimes use the term Equine COPD when referring to Equine Asthma in this article.

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Signs of Equine COPD

The most common signs of the condition are:

  • Exercise intolerance
  • Poor performance
  • Chronic cough
  • Nasal discharge
  • Excess mucus production

Horses with equine asthma may have a common clinical presentation among moderate to severe cases but will vary in severity, prognosis, and triggering events.

Mild cases tend to be harder to spot as some of these horses are virtually asymptomatic other than poor performance.

The following comparison of mild to moderate versus severe equine asthma is adapted from the ACVIM Consensus Statement 2016. [1]

Mild to Moderate Equine Asthma

Previous name: Inflammatory airway disease (IAD)

Age of Onset: < 7 years

History: Genetic component not studied. History of stabling or recent season change.

Clinical Signs:

  • Normal breathing at rest
  • Intermittent coughing, especially after exercise
  • Poor performance

Disease Progression: May resolve spontaneously or with minimal intervention. Low risk of recurrence.

A mild case of asthma can still be harmful to the equine athlete. Even mild or asymptomatic horses can have lasting effects of poor performance and cough from EA.

One study suggests that in the racehorse population, even mild asthma is detrimental to performance based on inflammatory cells found in bronchoalveolar lavage (BAL). [3]

Severe Equine Asthma

Previous name: Recurrent Airway Obstruction (RAO)

Age of Onset: > 7 years; not exact, but younger horses tend to be mildly affected or asymptomatic

History: Possible genetic component. Dust allergens, history of stabling.

Clinical Signs:

  • Often dyspneic at rest
  • Flared nostrils
  • More persistent cough
  • Nasal discharge
  • Exercise intolerance
  • Presence of heave line

Disease Progression: May last weeks to months, with lifelong flare-ups. May improve with strict management and medication.

Causes and Risk Factors

The pathogenesis of the spectrum of equine asthma is still not completely understood; it is most likely to be multifactorial.

Severe equine asthma (previously COPD or heaves) is thought to be triggered by environmental allergens – beta-glucans in mold, dust, and endotoxins present in hay, shavings, and straw. [12]

Horses that are predominantly stalled rather than on pasture are thought to be more affected by these triggers. Even the cleanest barns can be loaded with endotoxins and mold spores.

When we think of dust sources in a stalled horse’s environment, the main offenders are bedding and feed.

Fungal spores are found in all hay, regardless of quality. The degree to which the hay is contaminated varies based on the hay’s temperature at the time of baling.

Hay and straw increase the dust levels in the horse’s environment by 6-7 times compared to just the stall itself. [4]

Risk Factors

One study showed a possible regional distribution of risk factors for horses in the United States. In the northeast U.S., moldy hay is a typical trigger. In the southern part of the country, horses are more likely to be affected by pasture allergens. [5]

Keep in mind that any horse can be affected, especially if there has been a recent feed or environmental change.

Some viruses and bacteria have been linked to equine asthma including influenza, equine herpesviruses (EHVs), Streptococcus equi, Pasteurella species, and Actinobacillus species.

It is unclear whether these infections are secondary to asthma and weakened immune defenses or a primary cause for asthma. [5]

Diagnosis of Equine Asthma

Diagnosis of equine asthma is often suspected after a thorough history and exam. A comprehensive review of management and feeding practices might indicate possible triggers.

Any changes in the environment (recent seasonal changes, brought in from pasture to stall, air quality, etc.) should all be addressed, as well as any changes in feed or hay.

Recent respiratory illnesses should also be discussed. However, history may be less likely to help make a presumptive diagnosis in mild and subclinical cases, which typically require additional diagnostics.

Thoracic Auscultation

A thorough exam will also include thoracic auscultation – listening to all lung fields and trachea. Auscultation is often repeated with a rebreathing bag to encourage the horse to take deeper breaths. Crackles and wheezes indicate possible respiratory disease.

Unfortunately, thoracic auscultation is insensitive in identifying pulmonary disease in horses due to their thick chest wall so cannot be relied on exclusively to determine pulmonary changes. Less than half of horses with severe EA were found to have abnormal thoracic auscultation.

Tracheal Endoscopy

The veterinarian may perform tracheal endoscopy to assess m