Respiratory Disorders in the Horse

The Equine Respiratory System

At Virginia Tech's Marion duPont Scott Equine Medical Center, a variety of treatments are available for correcting disorders of the upper respiratory system and improving the odds of performance success. Equine upper respiratory disorders often have clinical signs such as labored breathing, flared nostrils, and strange noises during exercise. These conditions can be detrimental to an equine athlete's health and can also inhibit performance during competition.

"Respiratory disease is probably second only to lameness in terms of performance limiting illnesses in horses," said Harold McKenzie, DVM, MS, Dipl. ACVIM, assistant professor of equine medicine. "The function of the respiratory tract is gas exchange--getting the oxygen in, getting the carbon dioxide out--so anything that limits the flow of air is likely to impair athletic ability." (For more on respiratory tract anatomy and function, see The Airways and Lungs.)

Although all horses can suffer from diseases affecting the nasal passage, larynx, soft palate, pharynx, and sinuses that comprise a horse's upper airway system, these conditions predominantly affect athletes competing in racing, dressage, hunting, jumping, polo, driving, and other disciplines.

"Performance horses go out and train at high-speeds and breathe at a faster rate to keep up with oxygen debt," said Nat White, DVM, MS, Dipl. ACVS, the Jean Ellen Shehan professor and director of the center. "Any problems with air flow due to soft tissue damage or control of the upper airway movement can cause increased noise during breathing and a lack of oxygen reaching the lungs."

The most common upper airway complication that Ken Sullins, DVM, MS, professor of equine surgery, has seen in his patients is laryngeal hemiplegia, also known as "roaring," which is acquired as a result of trauma to the left recurrent laryngeal nerve. Other issues that frequently reduce air flow include dorsal displacement of the soft palate, pharyngeal collapse, airway obstruction, pharyngeal lymphoid hyperplasia, entrapped epiglottis, and arytenoid chondritis.

"The causes vary from inflammatory conditions to degeneration of nerves that control upper airway function," said Sullins. "The upper airway is very sensitive to irritation and significant issues stem from airway turbulence during exercise when the throat is inflamed."

According to Sullins, when a patient at the Marion duPont Scott Equine Medical Center is presented with an upper respiratory problem, the diagnosis is usually based on an analysis of the animal's health history, a physical exam, monitoring during exercise on a high-speed treadmill, and imaging of the upper airway system by ultrasound and standing video endoscopy. Other imaging technologies, including nuclear scintigraphy, ultrasound, and digital radiography, might be also be used if further visuals are required.

Although medical therapy is available for some of these maladies, surgical intervention is often required.

"Fundamentally, most, if not all, upper respiratory problems are mechanical in nature and therefore tend to be treated through structural repairs," said McKenzie. "So if something is obstructing the flow of air, you can suture it back or remove it and the problem goes away."

Further research is needed in order to pinpoint the specific causes of many upper airway complications in performance horses. However, the specialists who study the diseases have their own theories.

"There seems to be a geographical component for some laryngeal infections," said Sullins. "We suspect that it might have something to do with racetrack surfaces or air quality in specific areas. Certainly horses that race on turf have reduced incidence of this type of problem."

Information regarding the Marion duPont Scott Equine Medical Center's clinicians and services is available online at www.vetmed.vt.edu/emc. Consultations can be scheduled by calling 703/771-6800.

Virginia Tech's Marion duPont Scott Equine Medical Center is a premier full-service equine hospital located in Leesburg, Va., that offers advanced specialty care, 24-hour emergency treatment and diagnostic services for all ages and breeds of horses. One of three campuses that comprise the Virginia-Maryland Regional College of Veterinary Medicine, the center and its team of equine specialists are committed to providing exceptional treatment to patients, superior service to clients, and cutting-edge research to the equine industry.

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