Owners prove astute observers of asthma signs in horses – study

Owners can be reliable evaluators of clinical signs of asthma in horses over time, especially in relation to coughing, researchers have found.

In fact, the owners of horses with mild to moderate asthma were more likely than veterinarians to discern respiratory effort, although the owners of horses with severe asthma were not.

“As horses with mild asthma, by definition, have no respiratory effort at rest, it may be that the owners actually referred to the increased respiratory effort during or shortly after exercise that these horses often experience,” Tyler-Jane Robins and her fellow researchers noted in the journal Animals.

Equine asthma is a chronic non-infectious inflammatory disease of the lower airways. It is a pervasive and important cause of poor respiratory health in horses.

Clinical presentation ranges from mild reductions in peak performance to crippling respiratory impairment.

Horses with severe asthma may be diagnosed using clinical scoring alone, but more subtle disease often requires lung function testing and laboratory evaluation of lower airway respiratory secretions to arrive at a correct diagnosis.

Robins, working with Daniela Bedenice and Melissa Mazan, all with the Cummings School of Veterinary Medicine at Tufts University in Massachusetts, observed that there are few published studies describing the course of asthma over time.

In their study, they looked at horses with at least two visits for asthma evaluation to the specialty pulmonary clinic at the university’s hospital for large animals.

They also described and quantified the types and range of clinical presentations for equine asthma, examined the reliability of owner perception of clinical signs through a newly developed owner complaint score, and looked at the diagnostic methods used, as well as the response of horses to both treatment and the passage of time.

Horses included in the study had visited the clinic between 1999 and 2023.

The study team excluded 936 horses, either because they had only one visit to the clinic for asthma evaluation or there was inadequate documentation.

A total of 76 horses were included in the study, who between them had 197 clinic visits for asthma.

Of the 197 visits, 138 (70%) resulted in a diagnosis of mild to moderate asthma and 45 (22.8%) resulted in a diagnosis of severe asthma.

The information in the horse case files was analyzed for agreement between owner complaints (based on the complaint score) and clinical examination findings. The complaint score focused on the client’s perception of the horse’s problem, rather than on the observations made by a veterinarian.

The comparison between complaint scores and veterinary examination results, which were also scored, showed that the owners were more likely than veterinarians to detect coughing — and a decrease in cough was the most common owner observation after treatment.

Owners and veterinarians were generally in agreement on a patient’s clinical picture, the study team found.

The results even raise the question of whether owners, who have the benefit of more observation time, were actually more reliable observers than the veterinarians.

Further, the researchers found that tests of airway hyperreactivity proved more successful in detecting changes in mild or moderate equine asthma than baseline lung function testing and assessment of the content of lung lavages.

Notably, of the 76 horses included in the study and across the 197 visits, only one horse ever presented with a fever.

“This aligns with the current understanding of equine asthma and the consensus that most affected horses do not have a fever unless a secondary respiratory infection has occurred.”

The authors said the information about the pharmaceutical treatment of equine asthma that emerged from their study is also relevant.

The fact that asthmatic horses, with either the mild or severe form, are prescribed inhaled steroids more than any other drug is not surprising, given that both inhaled and systemic corticosteroids have been shown to improve lung function in horses with severe asthma.

However, the finding that severely asthmatic horses are much less frequently prescribed systemic steroids than mild to moderately asthmatic horses is interesting, they said.

This difference may represent the reported demographic differences of typical cases. Horses with severe asthma tend to be older, whereas horses with milder asthma are usually younger or middle-aged. Indeed, this demographic difference was observed in the study horses.

“The decreased prescription of systemic steroids in the severely asthmatic horses may therefore reflect the clinicians’ wariness to prescribe these medications to patients who may be more predisposed to (or more likely to already have) concurrent diagnoses that make them more sensitive to the side effects of systemic steroids.”

It is also interesting to note, they said, that no systemic bronchodilators were prescribed to the asthmatic horses after their first visit to the hospital, regardless of disease severity, whereas inhaled bronchodilators were commonly prescribed to both groups of patients (but especially the severely asthmatic horses).

In conclusion, the researchers said veterinarians could leverage the good observational data from owners of asthmatic horses in what they described as “team-based” veterinary healthcare.

The horses who came to the hospital and were treated improved with treatment and/or time, based on several levels of assessment, including the views of owners. The findings, they said, illustrate the largely positive effects of treatment.

Specifically, owner complaints of cough may be an especially reliable way to track equine asthma improvement and may be more useful at tracking improvements over time than examining the contents of lung lavage fluid.

Robins, T.-J.; Bedenice, D.; Mazan, M. A Longitudinal Analysis of Equine Asthma Presentation and Response to Treatment Using Lung Function Testing and BAL Cytology Analysis in Combination with Owner Perception. Animals 2023, 13, 3387. https://doi.org/10.3390/ani13213387

The study, published under a Creative Commons License, can be read here.