Horses with severe asthma have clinical signs while standing or walking. | Adobe Stock

Q: What is the difference between mild/moderate and severe equine asthma based on clinical signs and respiratory function?

A: Horses with mild to moderate asthma tend to not have respiratory signs at rest. They do not cough or have an increased respiratory rate or effort at rest. But they might cough at the beginning of exercise, or they might be a little slow to recover. They might not perform at exactly the level you want them to, but you’re not sure why. These horses have mild to moderate degrees of inflammation in the airway. 

So, when we sample the lower airway through a procedure called a bronchoalveolar lavage (BAL), they have evidence of increased inflammation, but not to a very severe degree. When we count the immune cells in there, it’s a lower number than in a severe case. 

The severely asthmatic horses have clinical signs at rest such as coughing while standing or walking around and increased respiratory rate and effort at rest. When we sample the airway, there are more substantial degrees of inflammation. Various cell types can be involved, but there’s a lot of inflammatory cells present. Veterinarians can also do different types of pulmonary function testing, which can help them classify the severity.

Not every horse with mild-moderate disease develops severe asthma. Some horses with mild-moderate asthma can be resolved and never develop severe disease.

Over the last 20 years, naming and classification of equine asthma has changed significantly. Historically, we talked about asthma as heaves, and then it became recurrent airway obstruction. Sometimes people might say COPD. There was a time when we used recurrent airway obstruction and inflammatory airway disease to describe these horses. Inflammatory airway disease was essentially the subset of horses that now we call mild to moderate asthma where they don’t have signs at rest, and they tend to be younger horses. Sometimes they’re the racehorses or the younger performance horses, whereas with recurrent airway obstruction, most of the information written about that now translates to severe equine asthma cases.

 

Related Content | Ask TheHorse Podcast: Managing Asthma in Horses

About the Experts:

Picture of Kelsey A. Hart, DVM, PhD, Dipl. ACVIM (LAIM)

Kelsey A. Hart, DVM, PhD, Dipl. ACVIM (LAIM)

Kelsey A. Hart, DVM, PhD, Dipl. ACVIM (LAIM), is a professor of large animal internal medicine and Hodgson Chair of equine studies at the University of Georgia’s College of Veterinary Medicine, in Athens. She received her DVM from Cornell University, in Ithaca, New York, in 2004. She completed an internship and a residency in large animal internal medicine and a PhD in endocrinology at the University of Georgia. Hart’s research centers on immune-endocrine interactions during illness, and the diagnosis and treatment of equine sepsis and endocrine diseases.

Picture of Kate Hepworth-Warren, DVM, Dipl. ACVIM

Kate Hepworth-Warren, DVM, Dipl. ACVIM

Kate Hepworth-Warren, DVM, Dipl. ACVIM, grew up in Indiana and graduated from Purdue University, in West Lafayette, Indiana, in 2010 with her DVM. Following graduation, she did an internship in Florida and then moved back to the Midwest for an equine internal medicine residency at Iowa State University (ISU), in Ames. After achieving board-certification in large animal internal medicine, she stayed on for a year at ISU and then spent four years in private practice in New Jersey. In June of 2019, she accepted her current position as associate professor at North Carolina State University, in Raleigh, and moved south. Her favorite type of cases are neonatology, respiratory disease, and neurology.