An older pasture pet with severe equine asthma is predisposed to recurrent bouts of pneumonia

The term “equine asthma” captures all horses with noninfectious respiratory conditions ranging from mild inflammatory airway disease to severe asthma, the latter of which was previously referred to as heaves, chronic obstructive pulmonary disease (COPD), or recurrent airway obstruction (RAO). Although related, this spectrum of diseases is not necessarily continuous, meaning horses with mild or moderate equine asthma don’t necessarily progress to the severe form.

When horses are affected with severe equine asthma (SEA), classic clinical signs include frequent coughing, exercise intolerance, increased respiratory effort at rest, and a heaves line—a ridge of enlarged abdominal muscles that runs diagonally from the point of the hip forward to the lower edge of the ribs.

You might be aware of the many factors that can contribute to the development of SEA, most notably inhalation of dust, mold, and endotoxin particles generated by either hay or the environment. But have you ever considered secondary illnesses that can affect asthmatic horses? In this case report we see how a senior horse diagnosed with severe equine asthma repeatedly developed pneumonia.

Anastacia’s Asthma ­Adventure

Anastacia, a 22-year-old Thoroughbred mare, was examined by veterinarians at Hagyard Equine Medical Institute, in Lexington, Kentucky. Her owner, Ashley Watts, who runs a hunter/jumper boarding and training business called Liftoff Equestrian, in Versailles, Kentucky, said “Anna” had trouble breathing the previous summer and pneumonialike symptoms the past few winters. Watts’ primary veterinarian referred her to Hagyard for an examination with an internal medicine specialist.

“Before my appointment I thought it was really bad heaves, and I was worried the doctor at Hagyard was going to recommend euthanasia,” says Watts.

A complete physical examination of Anna revealed an increased respiratory rate and effort and flared nostrils with each breath. She had a heaves line, indicating a marked abdominal effort to breathe. Her heart rate was also moderately elevated, but she did not have a fever at the time of presentation. In addition, she appeared mildly dehydrated.

Auscultation (listening with a stethoscope) of the lungs revealed decreased airflow to both the right and left lung fields.

“In addition, (we heard) wheezes, which indicate narrowing or constriction of the airways, and pleural friction rubs, which are generated as the roughened surface of the lung rubs against the pleura—lining of the thorax, or chest,” says Nimet Browne, DVM, MPH, Dipl. ACVIM, an internal medicine specialist at Hagyard.

Bloodwork revealed a very mildly elevated white blood cell count, while serum biochemistry was within normal limits.

“Cases of equine asthma can have normal or high white blood cell counts, whereas pneumonia cases typically have elevated white blood cell counts,” says Browne. “So, seeing only a slight elevation in white blood cells was a little atypical.”

An ultrasound examination of the chest revealed a broad-based comet-tail artifact along the right side of the right lung, indicating pleural roughening or abnormalities in the lung surface. In addition, a larger, 2-centimeter circular area of consolidation indicated a region of the lung that was not aerated properly.

“Unfortunately, the one drawback of ultrasound is that it cannot penetrate air,” explains Browne. “Therefore, it can only show us abnormalities on the surface of the lung. If there are further abnormalities deeper within the tissues, only radiographs (X rays) can identify those. Even though there were decreased lung sounds with wheezes bilaterally (in both lungs), only the right (lung) had evidence of lung changes.”

Based on these results, she diagnosed Anna with an equine asthma crisis and right-sided pneumonia. Browne says asthma causes widespread bronchoconstriction as well as a moderate increase in mucous production. At the same time, the normal mechanisms of clearing the airways of normal debris and mucus are not working, so these horses are predisposed to developing pneumonia. Pneumonia can be relatively mild, as in Anna’s case, or much more severe, leading to pleuropneumonia (fluid accumulation within the chest cavity).

Although not performed in this case, ­additional testing to confirm pneumonia could include chest X rays and a transtracheal wash (in which the veterinarian flushes sterile saline into the trachea, aspirates the fluid with tubing and a syringe, and evaluates it). The population of white blood cells in the transtracheal wash can help confirm ­pneumonia, and culturing the wash fluid can help veterinarians identify the bacterial origin of the disease. Culturing can also help identify the most appropriate antibiotic to prescribe.

“In this case, the mare’s clinical signs were so severe at the time of presentation that the transtracheal wash was not ­performed due to concerns that the ­procedure may exacerbate her clinical signs,” says Browne. “Thus, we elected to treat with broad-spectrum antibiotics.”

She adds, “And while a diagnosis of equine asthma requires performing a procedure called a bronchoalveolar lavage (a lung wash), this test also could not be performed in this mare due to the severity of her clinical signs.”

Anna’s Medical Management

Anna was hospitalized at Hagyard and treated with intravenous fluids, broad-spectrum intravenous antibiotics, and anti-inflammatories (flunixin meglumine) for the pneumonia. Browne prescribed the bronchodilators albuterol and ipratropium bromide to address the asthma via ­nebulization.

“We used the Flexineb to deliver the nebulized medications,” says Watts. “Anna accepted the mask easily, and you could tell she felt better afterward.”

Browne also advised Watts to offer Anna a dietary omega-3 fatty acid supplement, which researchers have found can improve horses’ clinical signs and lung ­function.

“The most common treatment for equine asthma is systemic corticosteroids to control the lower airway inflammation associated with the disease process,” she said. “However, systemic corticosteroids can have many unwanted side effects, with the most severe being laminitis. This mare was an older horse with a history of laminitis and was suspected to also have pituitary pars intermedia dysfunction, also known as equine Cushing’s. As a result, systemic corticosteroids were withheld.”

Watts says Anna did very well at home with daily nebulization moving forward, requiring corticosteroids only sparingly for severe asthma flare-ups. She was able to taper the mare’s nebulizer sessions back to weekly over time.

An Internist’s Perspective

“Equine asthma is a common respiratory disease of horses that can occur in all breeds and performance disciplines,” says Browne. “Mild to moderate equine asthma is seen in up to 60% of horses in some environments, while the prevalence of SEA is closer to 15%. The recurrent cough and increased respiratory effort are attributable to constriction of the airways, mucous hypersecretion, and airway inflammation following exposure to environmental triggers.”

Browne recommends decreasing forage-associated dust, mold, hay, and endotoxin exposures by thoroughly and properly soaking or steaming hay and feeding hay from the ground in a pan or a haynet hung outside a stall with an open top, as with a stall guard or Dutch door. In addition, she suggests feeding alternative forms of forage, such as haylage, chopped dry forage, alfalfa, silage, or completely cubed diets.

“In some cases owners may need to replace hay altogether and transition to a complete pelleted feed diet,” Browne says. “Each patient requires an individualized ­approach, and all of these strategies should be made after consulting with your veterinarian, as each horse’s case will be unique.”

Equine asthma, Browne cautions, typically requires long-term management with a combination of environmental and medical intervention, and some horses might require lifelong treatment. Such medications include anti-inflammatories, bronchodilators, and those that decrease mucous production and increase mucous clearance.

Summary

This case provides an example of how horses with uncontrolled SEA present to veterinarians and the aggressive therapy required to make them comfortable. The internists treated Anna with the highest level of care as outlined in the current American College of Veterinary Internal Medicine Consensus Statement.