Tying Up (Muscle Twitching and Cramping) in Horses

Key Takeaways

Muscle twitching and cramping, also referred to as “tying up”, are symptoms that appear from painful and continuous muscular contractions. 

• During a severe episode, horses might refuse to move and suffer from extreme pain

• Conditions more commonly associated with cramping include exhaustion, exertional rhabdomyolysis (ER), and electrolyte disturbances

• Diagnostics include blood work, urinalysis, a complete physical evaluation, and sometimes muscle biopsy

• Treatment is specific to the underlying condition, but general therapy involves muscle relaxation, pain medications, and fluid therapy

A Closer Look: What is Tying Up in Horses?

Muscle twitching and cramping often appear after exercise. Immediate care includes rest, dry hay, and a few days of light exercise while waiting for a veterinary professional evaluation.

Sporadic muscle twitching and cramping is more frequent in hot, humid weather as horses lose a great amount of fluids at a fast rate, causing deficits of electrolytes such as sodium, potassium, and calcium, which are required for healthy muscle and heart function. 

Prognosis varies depending on the severity of the case. Milder cases often resolve after a few days of rest or lighter exercise and dry hay feeding. Chronic cases generally need medical attention and medications such as muscle relaxers. 

Excessive muscle twitching and severe cramping is considered an emergency. Tying up can lead to severe kidney damage and heart conditions due to electrolyte imbalances and progressive muscle damage.

Possible Causes

The most common causes of muscle twitching and cramping in horses are:

• Exhaustion 

• Exertional rhabdomyolysis (ER)

• Polysaccharide storage myopathy (PSSM)

• Electrolyte imbalances

• Hyperkalemic periodic paralysis

Other causes might include:

• Hypocalcemia (low calcium; relatively rare)

• Shivers (a spastic condition of the limbs)

• Synchronous diaphragmatic flutter

• Ear-tick infestation

Risk Factors

In severe cases, such as chronic exertional rhabdomyolysis, horses might be unable to move, show colic-like symptoms, or become recumbent and unable to stand. In milder cases, such as sporadic ER, the patient might show a stiffer or stilted gait that usually disappears with rest.

ER can either be sporadic, specifically after excessive exercise, or chronic, if it happens repeatedly even after light exercise. Chronic ER might be caused by polysaccharide storage myopathy, malignant hyperthermia, and recurrent ER. These conditions are typically due to hereditary gene mutations or breed-related factors, affecting in particular Arabians, Morgans, and other light breeds.

Testing and Diagnosis

A variety of tests may be used to determine the underlying cause and consist of:

• Physical examination

• Genetic testing

• Bloodwork 

• Muscle biopsy

• Urinalysis

Treatment largely depends on the underlying condition. General supportive treatments include:

• Pain medications

• Muscle relaxers

• Fluid therapy

• Stall rest

Similar symptoms

Tying-up often can be mistaken for colic as it appears with several common symptoms, such as increased heart rate, rapid breathing, and excessive sweating.

Associated Symptoms

• Red or dark urine

• Excessive sweating

• Exercise intolerance

• Short, stiff gait

• Poor performances

• Quick, shallow breathing