By Dr. Cathy Barnette, a paid Consultant for Covetrus^®

While veterinarians have long regarded recurrent airway obstruction (RAO or heaves) and inflammatory airway disease (IAD) as two clinically distinct entities, these two conditions have been combined under the umbrella term “equine asthma.” ¹

Both conditions are related to underlying chronic airway inflammation, although the two presentations differ in clinical signs and severity. Signs of equine asthma may vary widely, ranging from a subtle decrease in cardiovascular performance to overt respiratory distress. In a performance horse with mild disease, the only clinical sign may be a delayed return to normal respiration after activity. ²

The horse’s significant respiratory reserve allows many horses to compensate for a surprising degree of respiratory disease without outwardly visible clinical signs. However, horses with traditional signs of heaves also exist, with flaring nostrils and labored, heaving breathing. ² This represents a more severe manifestation of equine asthma.

All horses with equine asthma have similar clinical signs (cough, excess mucus production, and poor performance), but there can be significant differences in the severity of those signs, as well as in triggers and underlying pathology. ¹

Diagnosis of Equine Asthma

Equine asthma is traditionally associated with poor air quality and airborne irritants. Severe respiratory inflammation typically affects stabled horses and has an underlying allergic component. ² While the allergic component of IAD has not been as extensively documented, inhaled irritants found in barns are also thought to play a significant role in this condition. ²

Triggers of respiratory inflammation in horses include pollen, dust, mites, ammonia gas (from urine), and particulate matter from gasoline engines (tractors, etc.). ^1,2 Fungi also play a significant role, especially in the case of summer pasture-associated severe equine asthma. ^1,2

Signs may wax and wane, depending on the degree of exposure to these airborne irritants. In severe cases of equine asthma, medical history alone may be sufficient to make a diagnosis. Clinical scoring systems can also offer benefits, both in diagnosis and grading severity. ¹ Pulmonary function tests are not readily available for equine veterinarians, as they are for the diagnosis of human asthma, but a clinical response to bronchodilators can also support a diagnosis. ¹ Upper airway endoscopy is recommended to rule out upper airway obstruction, and bronchoalveolar lavage and transtracheal wash can aid in the detection of inflammatory cells. ¹

Management of Equine Asthma

Equine asthma is a condition that is managed, not cured. Successful management requires close collaboration between the client and veterinarian, as you work with the client to optimize medical treatments and other management strategies. Medications can play a key role in decreasing the respiratory inflammation associated with equine asthma.

Inhaled and systemic glucocorticoids are commonly utilized, while other options may include mast cell stabilizers (such as sodium cromoglycate), low-dose interferon alpha, and nanoparticles of cytosine–phosphate–guanosine oligonucleotides (CpG). ³

Omega-3 fatty acids also play a role in managing chronic respiratory inflammation. Studies have demonstrated that omega-3 fatty acid dietary supplementation helps to alleviate clinical signs in both RAO and IAD. ³

Bronchodilators and mucolytic/mucokinetic agents may also prove beneficial, especially when combined with other measures.3 In addition to medication and nutraceuticals, management changes are needed to minimize the horse’s exposure to respiratory irritants.

Speak to your clients about the following strategies, implementing as many as possible to reduce airborne irritant exposure:

• Use low-dust feeds to reduce dust inhalation.
• Avoid feeding dry hay, instead feeding soaked hay or a complete feed.
• Use low-dust cardboard bedding or shavings instead of straw.
• Avoid the use of hay nets; feed horses from ground level.
• Improve barn ventilation by keeping doors open and promoting airflow.³

With these changes in housing and diet, horse owners can significantly reduce their horse’s exposure to respiratory irritants. This, in turn, can alleviate clinical signs and may help reduce a horse’s need for chronic medication.

Promote Client Communication

The long-term management of equine asthma requires close collaboration between a horse owner or trainer and their veterinarian. Frequent dialogue allows the detection of seasonal patterns in clinical signs, which may aid in the identification of triggers. Regular communication also allows you to make timely management recommendations, preventing the worsening or progression of signs.

Covetrus^® provides a number of tools to support communication, which can be beneficial when addressing equine asthma. Rapport^™, a multi-media messaging solution, allows you to remain in close contact with your equine clients through text messaging, email, and voice messaging. Additionally,

Covetrus Care Plans can support frequent veterinary exams while reducing the financial burden to clients. In horses with equine asthma, frequent examinations and regular client communication are essential components of management.

Summary

The term “equine asthma” encompasses a wide range of clinical manifestations, ranging from mild to severe. Management strategies may vary, depending on severity, but will likely require a combination of medical therapy and other forms of lifestyle management. Close collaboration with your clients is essential, in order to provide the best possible outcomes for these patients.

About the author Cathy Barnette, DVM is a veterinarian and freelance writer, based in Southwest Florida. After graduating from the University of Florida in 2006, Dr. Barnette spent 14 years working in small animal general practice. Her current professional focus is veterinary writing, creating educational content for veterinary teams and their clients. Dr. Barnette is a paid Consultant for Covetrus^®.

1. Couetil, L., Cardwell, J. M., Leguillette, R., Mazan, M., Richard, E., Bienzle, D., Bullone, M., Gerber, V., Ivester, K., Lavoie, J. P., Martin, J., Moran, G., Niedźwiedź, A., Pusterla, N., & Swiderski, C. (2020). Equine Asthma: Current Understanding and Future Directions. Frontiers in veterinary science, 7, 450. Retrieved from: https://www.frontiersin.org/articles/10.3389/fvets.2020.00450/full
2. Equine Asthma. Tufts Equine Center. Retrieved from: https://vet.tufts.edu/equine-center/services-specialties/respiratory-health/equine-asthma
3. Couëtil, L. L., Cardwell, J. M., Gerber, V., Lavoie, J. P., Léguillette, R., & Richard, E. A. (2016). Inflammatory Airway Disease of Horses--Revised Consensus Statement. Journal of veterinary internal medicine, 30(2), 503–515. Retrieved from: https://onlinelibrary.wiley.com/doi/full/10.1111/jvim.13824