Disease Du Jour: Equine Asthma

horse vet stethoscope
“Equine asthma is one of the more common causes of non-infectious respiratory disease in horses,” said Dr. Nimet Browne.

Equine asthma is one of those conditions that most veterinarians will see in their careers. How often or how severe will depend on many factors. Those can include the type of horses and their uses, wildfire smoke, allergens and management. Listen in as we talk with Nimet Browne, DVM, MPH, DACVIM, of Hagyard Equine Medical Institute, in this episode of Disease Du Jour.

“Equine asthma is one of the more common causes of non-infectious respiratory disease in horses,” said Browne.

Air Quality and Equine Asthma

Air quality issues can cause an increase in equine asthma, noted Browne. Asthma can be triggered by wildfire smoke. That means the smoke can trigger the horse to have transient asthma.

However, any inhaled particles—such as dust, mold or pollution—can cause or exacerbate equine asthma, she said.

“Equine asthma is a very recent term that encompasses a couple of different diseases that we used to refer to as inflammatory airway disease (IAD), or recurrent airway obstruction (RAO or heaves) or COPD,” explained Browne. “Those terms are now all lumped into the term equine asthma. I think that’s a better term overall as those diseases are likely on a spectrum of equine asthma.”

Browne went on to discuss the subtle differences in some of these asthma “subcategories” of disease.

Working Up an Equine Asthma Case

When asked about her method of working up a possible equine asthma case, Browne said one of the most important things is to “make sure it’s not an infectious cause of respiratory disease.”

She starts with a thorough physical exam that of course includes listening to the lungs. She described the differences in respiratory sounds for a variety of issues.

Browne said veterinarians might use a rebreathing test in some horses. This is where you put a bag over the horse’s nose to build up CO2 and to make the horse take long, deep breaths. “That exacerbates [respiratory] noises,” she said.

“If the horse has clinical signs at rest and an elevated respiratory rate, or coughs, or has abnormal lung sounds, you may not need to do a rebreathing exam,” Browne noted. “It may make their clinical signs worse, so I do try to avoid it in those patients.”

Browne also uses ultrasound and Xrays as part of some of her respiratory workups. Taking sterile samples from the airway (transtracheal wash using an endoscope) can help the practitioner make sure there’s not an infection on top of the asthma.

She also uses bronchoalveolar lavage (BAL). Brown said you can do this “blind” or with an endoscope. This provides a fluid sample from the lower airway for study.

Treatments for Equine Asthma

Browne covered a variety of possible treatments for equine asthma. She also discussed the different methods of using these treatments, such as IV, IM, oral or inhaled.

Treatment without changing management and environment will not give you a good outcome, Browne said. “You need to decrease the amount of inhaled dust and particles,” she noted.

Brown said that might mean the horse is turned out 24/7. Or the horse leaves the stall when it is cleaned or leaves the barn when owners are blowing the aisle. She recommended watering arenas where asthmatic horses are working to reduce dust. Avoid round bales of hay where horses like to bury their heads deep into the bale.

“There is a subset of asthma that is pasture-associated asthma,” said Brown. She said those cases are caused by allergens in the field. Management would be different for those horses.

Follow-up for Equine Asthma

“Most cases of severe equine asthma are chronic,” said Browne. That means they will have the disease for the rest of their lives.

While young horses with mild to moderate asthma can recover, most chronic cases need routine care. Browne said they also need a long-term strategy.

Training owners to be alert to what triggers asthma in their horses is important, said Browne.

“There is lots of new information on treating and managing equine asthma,” she said. “They are working on safer treatments and management strategies.”

Some of those might include hay soakers an steamers.

“The take-home is that this is not the end of the world for a horse,” Browne said. “We can get the horse better.”

About Nimet Browne, DVM, MPH, DACVIM

Dr. Nimet Browne studied veterinary medicine at University of Tennessee, graduating in 2010. Following veterinary school, Nimet went on to complete an internship in a private practice in Illinois, then a large animal internal medicine residency at Virginia Tech. During that time, she also obtained a Masters In Public Health with a focus on infectious disease. Following her residency, she completed a yearlong fellowship at Hagyard Equine Medical Institute. In 2016, she took a faculty position in the equine internal medicine department at North Carolina State University. Her interests include neonatal medicine, gastrointestinal disease, infectious disease and public health. She is currently working on manuscripts regarding infectious causes of diarrhea in neonates as well as the use on enrofloxacin in neonates.

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