Exercise Intolerance in Horses

Key Takeaways

Exercise intolerance is the decreased ability to tolerate strenuous exercise. 

• Recognized when horses are willing but unable to perform in routine training and conditioning

• Exercise intolerance is one of the first signs of exhaustion

• When persistent and unexplained, exercise intolerance may be a symptom of complicated underlying conditions like muscle disease, arthritis, respiratory illness, and heart disease; or any combination of the above

• Diagnosing the cause for exercise intolerance requires extensive testing

• Veterinarian assistance is required for diagnosing the cause and developing a treatment plan

A Closer Look: What is Exercise Intolerance in Horses?

Horses showing consistent exercise intolerance, without improvement over time, have an underlying health condition. Muscle disease and respiratory disorders are common. Some conditions associated with exercise intolerance are easily treatable through a change in diet, supplements, and training. Certain breeds have genetic predisposition, making them more susceptible to muscle disease. 

Arthritis is very common in horses, and once developed is a lifelong condition. The goal of treatment in these cases is to slow down the progress of the condition and increase quality of life. Exercise intolerance is associated with heart conditions, which are very rare and unpredictable, but can be fatal.

Possible Causes

Exercise intolerance may point to a number of different types of illness, including: 

Respiratory illnesses such as: • Paralysis of the larynx - laryngeal hemiplegia • Inflammatory airway disease

• Exercise induced pulmonary hemorrhage

Muscle disorders such as: • Myopathies • Exertional Rhabdomyolysis • Laminitis

Cardiac disorders such as atrial fibrillation and other arrhythmias

Musculoskeletal conditions such as osteoarthritis

Exhausted Horse Syndrome

Risk Factors

If caused by extreme exhaustion, exercise intolerance requires immediate vet assistance or the exhaustion can be fatal. Extreme signs of exhaustion in horses include: inability to move, dehydration, shock, colic, and diarrhea need ON SITE veterinary attention IMMEDIATELY. DO NOT MOVE the horse until cleared by a medical team.

Rapid onset of exercise intolerance, within one training session, is most likely exhaustion. Severity and frequency of exhaustion varies with the conditioning of the horse, diet, and environmental factors. Horse owners and trainers need to know the signs of extreme exhaustion as well as the behavior signals of the individual horses they are working with to prevent fatal complications. 

Intolerance associated with arthritis varies in severity. Horses can continue competing or be forced to retire early. While treatable, advanced stages of arthritis can cause lameness where euthanasia is the only treatment.

Testing and Diagnosis

Horses presenting with exercise intolerance will typically undergo the following diagnostics:

• Respiratory Exam • Lameness exam • Cardiac exam • Muscle Biopsy • Blood Work • Diet & Supplements

• New training regimen  • Surgery

Similar symptoms

Exercise intolerance is similar to lethargy and lameness

Associated Symptoms

Symptoms commonly seen with exercise intolerance include:

• Stiffness • Weakness • Unwillingness or inability to move • Anxious behavior, pain & excessive sweating

• Change in behavior • Increase in heart rate, body temperature & respiratory rate

Exhaustion Specific associated symptoms include: • Lethargy • Decreased appetite • Colic • Diarrhea • Hoof pain

Respiratory Specific associated symptoms include: • Roaring noise • Flared nostrils • Higher respiratory rate at rest

Muscle Specific associated symptoms include: • Firm, painful hindquarter muscles • Muscle tremors

• Stiff or spastic gait • Inability to collect • Abnormal canter transitions, inability to sustain normal canter

• Dark urine

Cardiac Specific associated symptoms include: • Bulging blood vessels • Stocking up of lower limbs

• Swelling of the abdomen