Equine Asthma, Taking Their Breath Away

Early diagnosis is key to effective management and treatment of equine asthma.

Nothing is quite as hard to deal with or creates as much panic as struggling to breathe. The same goes for our equine partners. The normal respiratory rate for healthy horses is 8-12 breaths per minute, but one suffering from equine asthma will struggle to breath and may cough, wheeze and have nasal discharge. The equine asthma label is the umbrella term to cover previously diagnosed conditions of inflammatory airway disease (IAD) and recurrent airway obstruction (RAO, or heaves). Veterinary Advantage magazine visited with Sarah M Reuss, VMD, DACVIM to discuss the basics of the disease and treatment options.

What is equine asthma?

“Equine asthma is a non-infectious inflammatory disease of the lungs of horses,” Reuss said. “It is quite similar to human asthma in that it can vary from only being an issue when exercising up through signs of respiratory distress at rest. In the same individual, signs may wax and wane over time.”

What are the signs/symptoms?

“With mild to moderate asthma, signs may only be seen with exercise where the horse is not performing up to expectations, can’t maintain exercise, takes longer to recover from exercise, or has a cough every time it exercises,” she said. “As it increases in severity, the horse may have signs at rest, including cough, nasal discharge (usually clear), increased respiratory rate and effort. When most severe, the horse will have such difficulty breathing that it loses weight.”

How is equine asthma diagnosed?

Veterinarians often diagnose asthma based on history and physical examination. This includes observing a cough, increased respiratory rate and effort without a fever or lymph node enlargement.

“To truly confirm the diagnosis and best characterize the disease, veterinarians perform a bronchoalveolar lavage,” Reuss said. “This involves collecting a wash of fluid from the lungs to look at the exact cell types present. While pulmonary function testing is the mainstay in human medicine, its availability in equine practice is very limited at this time.”

What causes equine asthma?

Inhaled particles in the environment – including dust, mold, fungi, pollens, and endotoxins – are the primary triggers for asthma.

“Particles less than 5um in size can reach the lungs and trigger inflammation,” Reuss said. “In its classic form, those particles are found in barns and stalls. There is a variant of asthma seen predominantly in the southeast United States called Pasture Associated Severe Equine Asthma, where horses suffer most in the late summer/early fall when exposed to pollens and fungi in the outdoor environment.”

Reuss added that each horse responds differently to the environmental triggers.

“Individual immune responses also play a role (all horses exposed to the same environment won’t all develop asthma),” she said. “We’re still learning more about these but in some families, there is a genetic component.”

The role of infectious diseases in equine asthma is still under review.

“We know human asthma can be exacerbated by the flu or other respiratory viruses,” Reuss said. “Evidence of a direct correlation in horses is lacking, but researchers are still looking.”

What are the best treatment options?

Because asthma is caused by factors in the environment, the most important treatment is to modify the horse’s environment to lessen exposure to whatever inhalant particles are triggering the horse. This may be easier said than done, but includes changes to feed, bedding, and housing, and will remain important for the rest of the horse’s life. Some horses do better living outside, but if they need to be stalled then straw should be avoided and replaced with low dust bedding like wood chips or cardboard. Dry hay (especially in round bales) should be replaced with soaked, steamed, or pelleted hay.

In addition, veterinarians have options for prescribing treatments.

“When environmental changes alone are not enough (or not possible), the use of glucocorticoids (steroids) should be the first drug choice,” Reuss said. “These can be administered either systemically or via inhalation. Boehringer Ingelheim recently launched a new product, the Aservo® EquiHaler® (ciclesonide inhalation spray), which is the first FDA-approved inhalant glucocorticoid for severe equine asthma. This product is targeted directly to the lungs with minimal systemic exposure and a beneficial safety profile.”

It is important to note Aservo EquiHaler has not been evaluated in pregnant or lactating mares. According to Reuss, in a large clinical field study, the most common adverse reactions reported were coughing, nasal discharge, sneezing, and nasal irritation/bleeding.

Reuss said a third treatment choice for when environment and steroids aren’t enough is the use of bronchodilators. These types of medications make breathing easier by relaxing the muscles in the lungs and widening the airways (bronchi).

“These help with symptomatic relief of the bronchoconstriction that is seen secondary to inflammation in the lungs,” Reuss said.

What is the prognosis for horses with equine asthma?

Veterinarians who treat horses with asthma can offer good news to horse owners that mild to moderate asthma can be fully reversible and horses can go on to lead totally normal athletic careers.

“We do know that with severe asthma, there can be remodeling of the lung tissue which may not be reversible,” Reuss said.

The earlier a horse can be diagnosed with asthma and undergo management changes and treatment, the better the long-term response.

“It’s important to remember, severe equine asthma is a lifelong condition that will require lifelong management and cannot necessarily be cured, but clinical signs can be managed to keep horses comfortable and in many cases still athletic,” Reuss said.

Photo credit: istockphoto.com/cmannphoto

Photo credit: istockphoto.com/soleg