managing equine asthma
On the surface, managing equine asthma—which comprises both recurrent airway obstruction (RAO, or heaves, an often-severe chronic condition common in older horses) and inflammatory airway disease (IAD, a mild inflammatory disease often seen in younger equine athletes)—might not seem too complicated: Modify the horse’s environment and treat, when needed, with corticosteroids and bronchodilators. In reality, however, it can be a real challenge.

At the 2017 American Association of Equine Practitioners Convention, held Nov. 17-21 in San Antonio, Texas, Melissa Mazan, DVM, Dipl. ACVIM, a professor at Tufts University Cummings School of Veterinary Medicine’s Hospital for Large Animals, in North Grafton, Massachusetts, reviewed how veterinarians can best treat and manage equine asthma.

Overall, treatment goals for both RAO and IAD are similar, Mazan said, but there are a few key differences.

She said goals for RAO should include:

  • Relieving bronchospasm that causes coughing and labored breathing;
  • Reducing lower airway inflammation;
  • Preventing acute episodes in the long term by controlling lower airway inflammation and obstruction; and
  • Returning the horse to athletic function.

For IAD, treatment goals should include:

  • Eliminating coughing and bronchospasm, which impair performance;
  • Reducing mucous production and airway obstruction;
  • Reducing airway reactivity; and
  • Preventing recurrences.

Mazan said effective treatment involves setting recognizable and attainable goals to which both the veterinarian and owner agree.

“Treatment of these diseases entails a team approach and an acceptance that this may be a lifelong problem that may be modified, but that is unlikely to go away,” she said.

“One of the most important aspects to successful treatment is the establishment of a reasonable definition of return to athletic use,” she added. “It is entirely reasonable to expect that a young racehorse (with IAD) would be able to return to racing after a short, targeted period of treatment. The owner of the older horse with heaves, however, must recognize that a much more modest return to light pleasure riding is a reasonable goal.”

It’s also important for veterinarians to consider the horse’s history before implementing a treatment and management plan, Mazan said. “For instance, if the history suggests that the horse is consistently worse in the spring, whereas clinical signs are abated in the barn in the winter, it may be that the worst culprits for this horse are molds and pollens associated with moist warm weather, and not the indoor environment that we commonly associate with heaves.”

A management plan for this horse might be very different than one for a pony that suffers more clinical signs when stalled than when turned out.

Pharmacologic Treatment

Corticosteroids Mazan called these drugs the cornerstone of successful treatment for both IAD and RAO.

Researchers have shown that systemic corticosteroids—administered orally or via injection—work well for treating horses with heaves, but appear less effective in IAD horses. Veterinarians use prednisolone and dexamethasone most frequently; triamcinolone is also effective in horses with airway obstruction, but is more closely associated with laminitis development in some horses than other corticosteroids, she added.

Veterinarians also have the option of using inhaled corticosteroids to treat IAD and RAO. Commonly used aerosolized drugs include fluticasone and beclomethasone. Veterinarians also have several metered-dose inhaler (MDI) options, including the Aerohippus and EquineHaler.

“A recent study compared the Aerohippus and the EquineHaler using a pressurized MDI and hydrofluoroalkane (propellant)-albuterol to elicit bronchodilation in horses with bronchospasm associated with exacerbation of heaves,” Mazan said. “There was no statistical difference in the decrease in pulmonary resistance—the ease with which air flows in and out of the lungs—produced by albuterol administration using the two different devices.”

She said the researchers found a more consistent response with the Aerohippus, and the Aerohippus appeared to show superior delivery of aerosolized particles to the lower airway (everything from the larynx to the lungs) compared to EquineHaler manufacturer data.

Depending on how severe a horse’s clinical signs are, a veterinarian might choose to begin treatment with systemic medications, or with a combination of systemic and inhaled aerosolized medications, said Mazan. With a chronic case he or she might opt for aerosolized delivery.

“The decision as to which delivery method is preferable may be influenced by a number of factors, including financial, given that aerosolized drugs and their delivery devices are quite expensive.”

Bronchodilators Veterinarians most often use aerosolized bronchodilators because they produce fewer side effects, Mazan said, but systemic options are also available. There are two types of bronchodilators:

  • Β-2 agonists, including albuterol (aerosolized) and clenbuterol (oral); and
  • Parasympatholytics, such as ipratropium (aerosolized) and hyoscine butylbromide (injection).

Veterinarians must evaluate each horse’s history and needs to determine which bronchodilator is best suited to the patient.

“A very important caveat, however, is that using corticosteroids (and bronchodilators) without remediating the environment is like using hand sanitizer without washing your hands,” Mazan said. “It’s better than nothing, but much less effective than removing the actual problem.”

Adjusting the Environment

“The barn environment is replete with organic particulate matter, respirable endotoxins, molds, and volatile gases such as ammonia,” Mazan said, all of which can—and often do—wreak havoc for horses with heaves. She offered tips for improving the environment for these horses:

  • Hay is notoriously dusty. If possible, switch to pelleted hay, complete feed, or silage. If you must keep using hay, feed it from the ground—not a haynet or rack—which decreases horses’ exposure to irritants and allows the respiratory system to work most effectively. Additionally, soak or steam it first.
  • Avoid storing hay above stalls, as this can expose the horse to even more respiratory irritants. If this is unavoidable, place a tarp on the floor below the hay to reduce dust and allergen exposure.
  • Grains and other concentrates aren’t immune to being dusty. If this is the case with your feeds, wet or soak it prior to offering it to your horse.
  • Like hay, straw is inherently dusty. Wood shavings and other low-dust beddings are preferable for horses with asthma.
  • Dampen aisleways before sweeping or raking, and avoid using leaf-blowers to clean aisles.
  • Remove horses from the barn before cleaning stalls, moving hay, sweeping, raking, and performing other chores that kick up dust.
  • Keep barns and stalls free of cobwebs and other materials that collect dust.
  • Leave barn doors and windows open whenever possible to allow for good ventilation and air movement.
  • Use low-dust footing in arenas, if possible. Remedy current footing by adding a humectant or hygroscopic agent to reduce dust.

Take-Home Message

Medical treatment and environmental management go hand-in-hand when you’re managing horses with asthma. Work with your veterinarian to implement the treatments, management techniques, and environment changes most suitable for your horse.

Mazan encouraged practitioners to monitor the outcomes of treatments and changes to ensure horses are improving. Lack of improvement could suggest an infectious disease and the need for additional diagnostics and treatment.