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obstructive pulmonary disease has been diagnosed and researched in horses since the 1970s, but this term is now outdated.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

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 pathogoenesis 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 are 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 bailing. 

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 county, 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 mucus production.

This involves visualizing the trachea and accumulation of mucous by inserting a camera through the nose and down the windpipe. The accumulation of mucous is scored on a scale of 0 to 3.

Tracheal aspirance samples can also be taken to measure the level of immune cells present in the trachea as an indicator of inflammation. [13]

Bronchoalveolar Lavage

A bronchoalveolar lavage (BAL) is thought to be the gold standard for cytologic evaluation of the airways as it allows deeper assessment of the bronchioles and alveoli. A tracheal wash alone is often insufficient since the representative cells at the trachea and upper airways are not the same as those found in the lower airways. 

Bronchoalveolar lavage testing in horses with EA has revealed increased mast cells, neutrophils, and eosinophils in affected populations.

Different populations of cells acquired from BAL may indicate different etiologies and predisposing factors in various groups of horses. For example, mast cells are more common in younger horses and may correlate to impaired performance. [3]

Radiographs

Radiographs are not a commonly used diagnostic tool since they are neither sensitive nor specific enough to diagnose EA. 

Prevention & Treatment

Because there is no cure for equine asthma, prevention and remission will rely on diligent environmental management and appropriate medication as indicated. Medication alone will not completely relieve symptoms in the most severe cases. 

Environmental Management

Environmental hygiene plays a critical role in the pathophysiology of equine asthma. Management can be divided into three broad categories: bedding, feeding, and ventilation. 

Bedding

To minimize mold spores and dust, use low-dust bedding such as chopped paper, rubber mats, peat bedding, and special wood shavings.

Straw is common in deep bedding systems, but even straw that is clean to the visible eye can still be contaminated in inadequately ventilated stalls and barns.

One study demonstrated horses stalled with baled peat bedding had fewer neutrophils on bronchoalveolar lavage than those stalled with straw pellets. [6] This indicates less allergen exposure and reduced immune response.

Feeding

Horses fed hay in stalls (versus those exclusively on pasture) are at risk of fungal spore exposure since all hay has some degree of fungal contamination. The amounts, though, will depend greatly on the moisture content at the bailing time. [7]

Square-baled and round-baled hay may affect horses differently, especially those with respiratory issues.

In one study, horses eating square-baled hay had more neutrophils in their airways (based on BAL samples), followed by horses fed square-baled hay. Horses exclusively on pasture had the fewest neutrophils in BAL samples. [8]

Pellets and cubed feed products provide a lower dust content hay alternative for stalled horses affected by EA, but may not be an ideal replacement for hay. 

Some experts recommend soaking hay in water to reduce dust content. Previous studies found that soaking hay for 30 minutes reduced respiratory problems for horses with heaves. [9]

Soaking hay may not wholly relieve all respiratory symptoms, however; and prolonged soaking reduces its nutritional content due to leaching out of soluble nutrients. 

Feeding at ground level allows natural respiratory clearing mechanisms. One study showed feeding hay from a net or other elevated position increased dust exposure 4-fold, while another study did not find a significant difference in respirable dust. [3]

Ventilation

Ventilation is a critical factor in minimizing dust exposure in stalled horses. Remember that a horse with EA will be affected by the surrounding stalls and walkways as well. Try to reduce cleaning and sweeping when affected horses are stalled. 

The affected stalled horse may show improvement within a week if moved to pasture (assuming the horse does not suffer from summer or pasture-associated airway disease). 

Medical Management

While medicines alone will not completely eliminate the respiratory symptoms of a horse with equine asthma, they can be used when in acute respiratory distress to help the horse breathe easier.

Typically, veterinarians will treat equine asthma with a combination of corticosteroids and bronchodilators. Corticosteroids decrease inflammation, and bronchodilators open the airways by relaxing airway smooth muscle.

Bronchodilators are especially useful in sudden onset attacks and can start working in less than an hour. 

These medications can be injectables, oral, or inhaled by masks or nostril devices. Inhaled options often have fewer systemic side effects than injectable or oral. 

Prognosis

While there is no permanent cure for equine COPD, affected horses can have a good quality of life with strict environmental modifications and control of flare-ups and symptoms.

The goals should be to manage the environment appropriately to minimize allergen exposure and to quickly and efficiently treat symptoms as they arise. 

Remember that recovery may be days to weeks following even a brief allergen exposure. Recovery time will depend on the severity of the initial symptoms, the horse’s age, and overall health.

In severe cases of equine asthma, there is structural remodelling of the airways from chronic inflammation that is irreversible. [10]

Many owners elect humane euthanasia of affected horses due to the cost of long-term treatment, recurrence and chronicity of symptoms, and emotional strain of often underweight and coughing horses. [11]

If your horse has been diagnosed with Equine COPD, consult with a nutritionist to formulate a low-diet diet that supports respiratory function. Submit your horse’s information online for a free consultation.

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References

  1. Couëtil, L. et al. Inflammatory Airway Disease of Horses—Revised Consensus Statement. J Vet Intern Med. 2016.
  2. Klier, J. et al. Comparison of Four Different Allergy Tests in Equine Asthma Affected Horses and Allergen Inhalation Provocation Test. J Equine Vet Sci. 2021.
  3. Ivester, K.M. et al. An observational study of environmental exposures, airway cytology, and performance in racing thoroughbreds.J Vet Intern Med. 2018.
  4. Woods, P.S. et al. Airborne dust and aeroallergen concentration in a horse stable under two different management systems. Equine Vet J. 1993.
  5. Couetil, L. et al. Equine Asthma: Current Understanding and Future Directions. Front Vet Sci. 2020.
  6. Moenki, J. et al. Effects of Bedding Material on Equine Lower Airway Inflammation: A Comparison of Two Peat Beddings, Wood Pellet, and Straw Pellet. Front Vet Sci. 2021.
  7. Art, T. et al. Environmental Control of Respiratory Disease. Int Vet Information Services. 2002.
  8. Robinson, N.E. et al. Airway inflammation in Michigan pleasure horses: prevalence and risk factors. Equine Vet J. 2006.
  9. Moore-Colyer, M.J.S. Effects of soaking hay fodder for horses on dust and mineral content. Anim Sci. 1996.
  10. Molet, S. and Hamid, Q. Role of Airway Remodelling in Severe Asthma. Severe Asthma, 2nd Ed. 2001.
  11. Couetil, L. and Ward, M.P. Analysis of risk factors for recurrent airway obstruction in North American horses: 1,444 cases (1990-1999). J Am Vet Med Assoc. 2003.
  12. Mintz-Cole, R.A. et al. Surface availability of beta-glucans is critical determinant of host immune response to Cladosporium cladosporioides. J Allergy Clin Immunol. 2013.
  13. Kusano, K. et al. Tracheal Endoscopic and Cytological Findings and Blood Examination Results in Thoroughbred Racehorses Suspected to have Lower Respiratory Tract Disease. J Equine Sci. 2008.