Horses can be affected by a variety of respiratory illnesses, both in the upper and lower respiratory tract. Although the clinical signs of each are similar, horse owners need to understand exactly what disease is affecting their horse so they can pursue timely and correct treatment.

The clinical signs of both upper and lower respiratory tract illnesses include nasal discharge, fever, lethargy, cough, respiratory noise, or exercise intolerance.

Diagnosing Equine Respiratory Disease

“Bloodwork and endoscopy (passing a small camera through the nose and into the airways) are usually the first diagnostic tools we use when respiratory disease is suspected,” said Megan Marchitello, DVM, clinical instructor of equine medicine at the Virginia-Maryland College of Veterinary Medicine, in Leesburg, Virginia, during a presentation on April 11, 2023.

With an abnormal endoscopy, veterinarians might observe swelling or mucus indicative of respiratory illness. They might also use dynamic endoscopy to observe the horse’s airway during exercise, she said. Radiography and ultrasound can help practitioners further check the airway. Ultrasound does not penetrate as deep as radiographs and only shows the surface of the lungs; however, radiographs can be more difficult to interpret.

Sampling the lower respiratory tract can help veterinarians determine exactly what disease is affecting the horse’s respiratory system. “Transtracheal wash is performed by injecting saline into the lower airway to get a sample to culture, which identifies pathogenic (disease-causing) bacteria,” said Marchitello. “This is a sterile procedure, which is why we are able to culture the sample.”

Veterinarians can use bronchoalveolar lavage (BAL) to identify the types of inflammatory cells in the distal (lower) airways, she said. This method is not sterile and, therefore, the samples cannot be cultured, but they can be used for cytology or PCR (polymerase chain reaction) testing.

Practitioners only perform thoracocentesis when the horse has signs of increased fluid in the chest cavity, said Marchitello. They use this procedure to collect fluid from the thoracic cavity outside the lungs for testing. Draining this excess fluid can also be therapeutic for the horse.

Equine Asthma: A Common Diagnosis

Equine asthma is one of the most common respiratory illnesses in horses and occurs when they react to environmental stimuli, causing lower airway inflammation, bronchoconstriction, hyperreactive airways, and increased mucous production, said Marchitello.

Horses with mild asthma might show clinical signs such as intermittent coughing and poor performance during work but appear normal at rest, and one course of treatment might be sufficient. Those with severe asthma are typically older than 7, show clinical signs at rest, and require long-term treatment and management, she added.

Veterinarians typically diagnose equine asthma through physical examination, CBC (complete blood count) testing, thoracic radiographs, and BAL cytology. Further evaluation might include ultrasound, endoscopy, or transtracheal wash if they suspect coinfection, said Marchitello.

Environmental modifications are vital when treating equine asthma. Owners of asthmatic horses should provide a low-dust feed near the ground, maximum time outside (if they don’t have pasture-associated asthma), and housing that’s separate from hay storage areas. They might also to wet hay to minimize dust and use a low-dust bedding option such as cardboard. “The main goal for (managing) horses with asthma is to remove the trigger, treat active inflammation, and control bronchodilation,” said Marchitello.

Medications such as corticosteroids, bronchodilators, mucolytics, and cell stabilizers and omega-3 supplementation can help veterinarians and horse owners manage equine asthma. Veterinarians most commonly prescribe corticosteroids because these drugs break down airway inflammation and can be inhaled to decrease the effects on the rest of the body.

Take-Home Message

Many respiratory illnesses can appear similar, said Marchitello. Therefore, it is important to pursue diagnostic testing to develop a more accurate treatment plan. “Early identification and treatment improve the overall outcome,” she said.