A rundown of respiratory diseases commonly observed in performance horses
It could be an airway noise while jumping, having difficulty performing upper level dressage movements, or laboring to finish a three-day event. The astute rider will notice different subtleties in his or her horse that might point toward a respiratory issue. The clinical signs can greatly affect a horse's maximal performance, and the diagnosis and appropriate treatment of an athlete's respiratory disease can be challenging. The following descriptions are to familiarize you, as the rider or owner, with common respiratory issues affecting performance horses.
Your Saddlebred has no problem racing through his paddock at full speed, but once asked to flex his neck and collect his trot in the ring, he has episodes of loud gurgling noises. Your horse likely isn't trying to avoid work, but rather he might be suffering from dorsal displacement of the soft palate (DDSP).
DDSP is a condition in which the caudal margin (back edge) of the soft palate is displaced over the epiglottis (a flap of cartilage at the entrance of the larynx), creating a performance-limiting and functional expiratory obstruction of the airway. The soft palate is the soft tissue at the back of the mouth that separates the nasal and oral cavities, and its position relative to the epiglottis relates to swallowing and breathing. During swallowing the soft palate moves upward and the epiglottis flips back, protecting the airway while directing food toward the esophagus. During exercise the soft palate should remain underneath the epiglottis to allow maximal airflow through the trachea. In DDSP-affected horses the outward rush of air during expiration causes the soft palate to billow upward and obstruct the airway. This respiratory condition is fairly prevalent and is a contributing factor in up to 8% of sporthorses and 35% of racehorses with poor performance.1
Clinical signs of DDSP include gurgling upper respiratory noise (described as "choking down" or "swallowing their tongue") and open-mouth breathing. "Upper respiratory noise is often a sentinel of underlying anatomic or functional abnormalities," notes Alfredo Romero, DVM, Dipl. ACVS, of Syracuse Equine Veterinary Specialists, in Manlius, N.Y.
Though it's most commonly seen in racehorses, DDSP can also affect Saddlebreds and Hackneys that are required to flex at the poll and other sport horses such as eventers that exert themselves during exercise. To diagnose the condition, veterinarians perform upper airway endoscopy while the horse is at rest, on a treadmill, or immediately after exercise. A newer portable endoscopy system now allows vets to examine horses' throats during exercise as well.
"With the advent of dynamic endoscopy, endoscopic evaluation is now possible during exercise under field conditions while the horse is performing his regular work," explains Mary Durando, DVM, PhD, Dipl. ACVIM, of Equine Sports Medicine Consultants, in Newark, Del. "The advantage of this type of examination over treadmill evaluation is it allows the rider to reproduce the conditions under which the horse has a problem, with the associated factors of bit, head position, rider and terrain that may be contributing to the condition."
Nonsurgical treatment options include rest and applying anti-inflammatory throat spray and/or using a figure-eight noseband, a restrictive bit in combination with tongue tie, or a throat support device. Restricting the tongue during exercise minimizes its backward push and, subsequently, the soft palate elevation and backward push of the larynx to a position that predisposes the horse to DDSP. When medical or tack interventions fail (nonsurgical success rate is 60%), surgical options include partial soft palate resection (trimming the caudal edge to create scarring and rigidity; success rate 50-60%), endoscopic laser palatoplasty (passing a laser through an endoscope to create defects in multiple areas along the caudal edge and promote scarring), myectomy (transection of the muscle that retracts the larynx; success rate 58-70%), and laryngeal tie-forward (suturing the larynx in a forward position; success rate 80-82%).2
Laryngeal Hemiplegia/Recurrent Laryngeal Neuropathy
You have a handsome 4-year-old Warmblood gelding that is a talented jumper. However, you recently noticed him emitting a whistling noise during exercise, and he seems to become winded quickly.
Laryngeal hemiplegia, commonly referred to as roaring, is the paralysis of one or both arytenoids (cartilages that form either side of the trachea entrance, abducting--or opening--during breathing), resulting in respiratory noise and decreased performance in 17-24% of racehorses and 8% of sporthorses.3 Typically affecting young large-breed horses, the condition is thought to originate from degeneration of the recurrent laryngeal nerve and results in muscle atrophy (wasting) and inability to move the arytenoid cartilage. The cause of this nerve degeneration can be idiopathic (unknown) or it might result from neck trauma, perivascular injection (injection of medications outside the jugular vein), guttural pouch infection, strangles, and plant or chemical toxicity.
Clinical signs of laryngeal hemiplegia are typically acute in onset and include inspiratory respiratory noise, exercise intolerance, and an unusual-sounding whinny. Veterinarians can make a definitive diagnosis based on endoscopy with or without an exercise or treadmill test. The degree of laryngeal hemiplegia is then classified on a scale from Grade I (normal) to IV (lack of movement of one of the arytenoids).
Most veterinarians recommend surgery to resolve this issue, with the type of surgery varying based on the grading classification and the horse's use. Surgeries include laryngoplasty ("tieback" surgery suturing the arytenoid; success rate 50-70%2), ventriculectomy/ventriculocordectomy (removal of excess tissue surrounding the arytenoids that interfere with the airway; more successful at reducing noise than airway flow), arytenoidectomy (partial ¬removal of the arytenoid when malformed from birth or when other corrective techniques have failed), and neuromuscular-pedicle grafting (in which a nerve is transplanted into the muscle for reinnervation). The latter procedure is typically selected for young horses with Grade 3 hemiplegia (slight movement, not full abduction of the arytenoids) that can afford the four- to five-month rest period it usually takes for reinnervation to occur. The success rate is approximately 50%.
"One advantage of this procedure over the others," states Romero, "is that if it ultimately fails to provide relief, it does not preclude the application of more traditional surgical approaches. Furthermore, complications such as postoperative aspiration, which are commonly associated with other surgical procedures that permanently alter laryngeal function, are avoided."
Inflammatory Airway Disease
Over the last few months your 5-year-old Dutch Warmblood eventer has exhibited a progressive cough, particularly during exercise. Recently, you have become more concerned because he has developed thick white nasal discharge and is struggling to complete cross-country courses.
Your horse could be affected by inflammatory airway disease (IAD), a condition occurring in 22-50% of athletic horses3 that can cause poor performance, mild exercise intolerance, or coughing. Affected horses are typically young, do not show increased respiratory effort at rest, and have milder clinical signs than those with heaves (recurrent airway obstruction, similar to human asthma). There is also an absence of any systemic signs of infection. Risk factors for IAD include exposure to excessive dust, debris, and noxious gases.
Veterinarians most commonly diagnose IAD through bronchoalveolar lavage, a diagnostic procedure in which fluid is flushed into and recollected from a portion of the lung and then analyzed to detect inflammatory cells. Vets further categorize IAD based on the type and number of ¬inflammatory cells present. According to Durando, these cases might be "best appreciated by endoscopic evaluation of the upper respiratory tract to look for large quantities of yellow or yellow-green tinged mucus. If present, a culture of the tracheal mucus can be performed (to help the veterinarian select the most effective ¬treatment)."
Treatment is aimed at limiting exercise, managing the horse's environment appropriately (e.g., limiting stall confinement and increasing turnout time, decreasing allergens in the barn environment), administering corticosteroids to alleviate ¬inflammation, and administering bronchodilators such as clenbuterol.
Exercise-Induced Pulmonary Hemorrhage
Your Quarter Horse gelding had a small tinge of blood in his nostrils last week after a barrel race. You dismissed it at the time, but now he is not hugging the barrels as usual, and you are concerned the blood might have something to do with his exercise intolerance.
Exercise-induced pulmonary hemorrhage (EIPH or "bleeding") refers to the blood present in horses' airways during intense exercise and can affect barrel racers, racing Quarter Horses, and as many as 93% of Thoroughbred and Standardbred racehorses.3 Although EIPH's etiology is unclear, the most widely accepted explanation is ruptured alveolar capillaries (small blood vessels within the lungs) due to the pressure of inspiration and increased blood pressure from intense exercise. The risk of developing EIPH increases with age, presence of tracheal mucus or dirt, and exposure to airborne particulates.
Veterinarians can diagnose EIPH via endoscopy if they observe blood in the airways 30-90 minutes following exercise, or by using bronchoalveolar lavage to detect red blood cells and cells containing breakdown products of red blood cells.
EIPH prevention methods target decreasing inspiratory pressure (correcting laryngeal hemiplegia or applying nasal dilator bands) and blood pressure. The diuretic furosemide (Lasix or Salix) is commonly used in racehorses to decrease blood volume and blood pressure and to attenuate bleeding.
Upper Respiratory Infection
Your horse came back from a show with a mild cough. A week later, although he is still bright and alert, he is now off his feed and has yellow nasal discharge.
Due to the stress of traveling, attending shows, and commingling with other horses, performance horses are particularly susceptible to acquiring upper respiratory viral and secondary bacterial infections. Spread through inhalation or contact with contaminated materials, upper respiratory viruses affecting horses include equine influenza, equine herpesvirus, equine viral arteritis (EVA), and rhinovirus. Clinical signs include fever, anorexia, cough, serous (clear, runny) nasal discharge, and edema (fluid swelling), and they typically develop one to five days (for EVA, sometimes as long as 14 days) following exposure. Viral infections usually clear up on their own and can be diagnosed presumptively using clinical signs or via culture and molecular testing of nasal swabs and blood. Horses are treated symptomatically with antipyretics to reduce fever and supportive care to ensure adequate hydration.
Most upper respiratory bacterial infections, with the exception of strangles, occur secondary to viral infections, which inhibit the normal clearance mechanisms of respiratory secretions. Bacterial infections often result in thicker, more purulent (producing pus) nasal discharge, depression, persistent fever, and bloodwork changes. Treatment includes rest, supportive care, and antibiotics.
Methods of preventing upper respiratory tract infection include administering immunostimulants (e.g., EqStim or Zylexis) prior to stressful events such as transportation and horse shows, and vaccinating horses to decrease the severity and duration of infection.
Respiratory disease is a common cause of decreased performance in horses. By recognizing the clinical signs associated with many of these common diseases, such as upper respiratory noise, bleeding, coughing, and fever, you can work with your veterinarian to quickly and effectively treat your equine athlete and return to doing the activities that you both enjoy.
1. Davidson E, Martin, BB. Diagnosis of upper respiratory tract diseases in the performance horse. Vet Clin Equine 2003;19:51-62.
2. Auer J, Stick, JA. Equine Surgery. Third ed. St Louis: Elsevier, 2006.
3. Kahn C. The Merck Veterinary Manual. Ninth ed. Whitehouse Station: Merck Sharp and Dohme Corp, 2011.
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