Exercise intolerance in horses refers to the inability or decreased capacity of a horse to perform physical activity at levels that are considered normal for its breed, age, or training status. This condition can stem from a variety of underlying issues, including cardiovascular, respiratory, muscular, or metabolic disorders. Identifying exercise intolerance involves assessing clinical signs such as poor performance, excessive fatigue, or abnormal recovery post-exercise. Diagnostic approaches often include physical examinations, exercise testing, and laboratory evaluations to determine the specific cause. This page aggregates peer-reviewed research studies and scholarly articles that explore the causes, diagnostic methods, and management strategies for exercise intolerance in equine athletes.
Reef VB, Roby KA, Richardson DW, Vaala WE, Johnston JK.Two dimensional ultrasonographic evaluation of the iliac arteries and terminal portion of the aorta was utilized in 18 horses with histories of exercise intolerance or hindlimb lameness. A plaque or thrombus was imaged in one or more of these vessels in 5 horses. In 2 horses, the initial rectal examination findings were normal and the thrombus may have been missed without the use of diagnostic ultrasonography.
McGuirk SM, Muir WW.Cardiac arrhythmias are probably more common in horses than in any other domestic animal species. The most frequent clinical complaint associated with cardiac arrhythmias is exercise intolerance. Physical examination is characterized by auscultation abnormalities such as fast or slow heart rate, irregular rhythm, extra sounds, long pauses, or abnormal heart sounds. The electrocardiogram is used to make a definitive diagnosis of the dysrhythmia. Other laboratory and cardiac function tests are employed to determine the etiology and to assess the significance of the arrhythmia. Antiarrhythmic the...
MacLean AA, Robertson-Smith RG.The upper respiratory tract of a pony mare with marked exercise intolerance and respiratory stridor was examined with a flexible fibreoptoscope. Both arytenoids were adducted and distorted. A diagnosis of bilateral chondritis of the arytenoids was made and confirmed at autopsy after surgery to enlarge the rima glottidis was unsuccessful. Other space occupying lesions of the rima glottidis are discussed and theories on the aetiology are postulated.
Haynes PF, Snider TG, McClure JR, McClure JJ.Chronic chondritis of the arytenoid cartilage was diagnosed in 7 male Thoroughbred horses examined for obstructive upper airway disorders. The history of the cases was characterized by a 3- to 6-month progression of exercise intolerance and inspiratory dyspnea during exercise. Endoscopy revealed marked asymmetry of the rima glottidis, partial or complete inability to abduct the involved cartilage, and axial displacement of the involved arytenoid cartilage. In less severe cases, the disorder was confused with laryngeal hemiplegia. Focal elevated lesions of the involved cartilage, which were fre...
Moorman VJ, Marshall JF, Jann HW.A 7-year-old sexually intact male Thoroughbred racehorse was evaluated because of exercise intolerance, respiratory tract noise, and coughing when eating. Results: A persistent dorsal displacement of the soft palate was identified during endoscopic examination of the upper portions of the respiratory tract. Radiography of the pharyngeal and laryngeal regions revealed a hypoplastic epiglottis that was ventral to, and not in contact with, the soft palate. The horse was anesthetized, and an oral endoscopic examination revealed a subepiglottic frenulum that had resulted in the dorsal displacement ...
Duggan VE, MacAllister CG, Davis MS.An 18-month-old Quarter Horse filly was evaluated because of dorsal displacement of the soft palate associated with epiglottic dysfunction that caused exercise intolerance and an abnormal respiratory noise. The abnormality of the epiglottis was corrected by use of a sedative dose of xylazine hydrochloride. There was no familial predisposition to hyperkalemic periodic paralysis, which may cause similar laryngopharyngeal signs, and the horse did not respond to administration of acetazolamide. There was no known history of trauma that could have caused neuritis, which has also been suggested as a...
Lilich JD, Gaughan EM.The diagnostic approach to the exercise intolerant racehorse depends on sound, fundamental steps to allow complete examination of the entire horse in a logical, time-efficient fashion. Availability of referral diagnostic modalities should not overshadow the need for collecting a clinical history or performing a complete physical examination. The diagnostic approach to exercise intolerance can be divided into a few basic steps. The first step, conducted without the horse, is a thorough discussion about the horse with the trainer and/or owner. Many clinical histories are complex and therefore fo...
Tetens J, Hubert JD, Eddy AL, Moore RM.A 2-year-old Thoroughbred filly was admitted to the hospital for evaluation of exercise intolerance. Resting videoendoscopic evaluation (i.e., while the horse was standing) of the nasopharynx and trachea revealed right arytenoid paresis and a tracheal defect that was 100 cm distal to the external nares. Surgery, consisting of a right prosthetic laryngoplasty, was performed. However, postoperative videoendoscopic evaluation revealed minimal abduction of the affected arytenoid cartilage. Dynamic videoendoscopic evaluation (i.e., while the horse was exercising) revealed the right arytenoid to be ...