Muscle Imbalance and Spasm in Horses


Introduction to muscle imbalance and spasm

The muscles of a horse’s body hold the backbone and limbs together in the correct position. Properly functioning, healthy muscles, therefore, are responsible for balanced posture and movements. Muscle imbalance is a common issue that affects the wellbeing of a horse. This causes deviation in posture and leads to sub-luxation of the skeletal joints, limiting joint movements.

It is important for the size and strength of the muscles on each side of the body to be symmetrical. If a muscle or group of muscles on one side of the body becomes weaker, stronger, looser, tighter, larger, or smaller than the corresponding muscle or muscles on the other side, this will cause muscle imbalance.

Muscle imbalance does not occur suddenly. It is a condition which often results from carrying out unbalanced exercises, exercising with improper form or bad posture, carrying out several daily life activities, and in very rare cases is congenital. Injuries, poor nutrition, and neurologic issues can also muscle imbalance in horses.

Muscle imbalance can lead to an unbalanced appearance, pain for the horse, limited movements, and instability. It also leads to an increased risk of injury to muscle, bone, joints, tendons and ligaments. Fatigue is the main cause of sports injuries in horses. This occurs when the horse moves in an unbalanced posture. Ensuring that muscles are balanced can relieve fatigue and prevent injuries.

Muscle spasm is a painful condition where a muscle or group of muscles contracts forcefully and involuntarily. When this condition occurs, the muscle can become unable to relax. Muscle spasm can occur in any muscle but most commonly occurs in the limbs and the muscles of the abdomen. A sustained muscle spasm is known as muscle cramps, and a condition where painful muscle cramps occur in the limbs is called charley horse. Muscle spasms in the horse’s back limbs are known as shivers. Equine shivering is characterised by periodic involuntary spasms of the muscles in the pelvic region, pelvic limbs, and tail. Sometimes forelimbs are also affected. Affected horses show stiffness, s sudden jerky extensor movements in the tail (tail elevation), and a tendency to move backwards.

There are many potential causes for muscle spasms in horses. Dehydration and electrolyte imbalance in the extracellular fluid is the most common cause. Excessive sweating causes dehydration and loss of electrolytes. Horses which have been intensely exercised in hot, humid weather conditions can suffer from a depleted water level in the body caused by sweating which takes place to help dissipate the body heat. Fluid loss occurs at a rate of up to 15-20L per hour when horses sweat. This can result in huge deficits in minerals like Sodium(Na), Potassium(K), Chlorine(Cl), Magnesium(Mg), and Calcium (Ca).

Otobius megnini ear tick infestation is another common cause of muscle spasms in horses.

Diagnosing muscle imbalance and spasms

In order to diagnose a muscle imbalance in a horse, a clinician will take into consideration information from the following sources:

  • The horse’s history
  • A physical examination
  • The horse’s biochemical profile (obtained via a serum enzyme test)
  • Urinalysis
  • Blood test
  • Electromyography (EMG)
  • Muscle biopsy
  • Genetic test

An informative history is required when assessing almost any disease in an animal. A history of any muscle problems such as cramping, pain and weakness, and the frequency of such problems is essential information. It is also useful for the clinician to know the animal’s exercise schedule, diet, vaccination and medication history, as well as all information relating to factors that are often precursors to muscle problems such as lameness, stress, and strenuous exercise carried out.   

There are a few characteristic clinical signs in horses suffering from muscle imbalance and spasm. These can be diagnosed via careful physical examination and palpation. Palpation of muscle mass provides important information about any muscle pain the animal is suffering, as well as swelling and muscle tone.

If a horse’s limbs are balanced, they will land in a perpendicular way as the horse moves. Observing the horse both while standing and while walking, therefore, can help identify any gait abnormalities which may indicate that the limbs are unbalanced. Shivering horses show tenseness and trembling of the hind limb, a sudden elevation of the tail, or a tendency to move backwards, picking up their feet. Muscle imbalance and spasms can very often result in lameness, and a lameness evaluation can be carried out by means of a flexion test. This test indicates if the animal is experiencing any muscle pain or problems with its joints.

Extremely fatiguing exercises such as endurance rides can cause increased creatine kinase(CK) level in the serum. The standard level of CK in serum is less than 1000U/L. A serum biochemical profile can determine the animal’s CK level. Measuring the levels of electrolytes and mineral concentration in the horse’s urine and blood can help to detect electrolyte imbalances in horses which are suffering from muscle spasms and cramping. For this diagnosis, urinalysis and blood tests can be carried out. Dehydration is the most common cause of muscle spasms and can be determined as part of these tests.

Electromyography (EMG) is a technique which detects muscle potential by placing a needle very close to the motor endplate. When muscle contract action potential occurs, this can be observed as a wave pattern in the EMG. If the horse is suffering from muscle spasms or cramp problems; this wave pattern will appear irregular.

Muscle biopsy is an important technique used to obtain diagnostic information regarding muscle problems. Genetic tests can also be used to help detect congenital myopathies in horses.

Different causes of myopathy

The word ‘myopathy’ is  defined as a disease of the skeletal muscles.  The major sign of this disease is muscle weakness which occurs due to dysfunction of muscle fibres. Other symptoms are muscle cramps, pain and stiffness. Myopathies can either be genetic or acquired. There are several myopathies that commonly occur in horses, all of which have several possible causes.

Types of Myopathies

  • Equine exertional rhabdomyolysis(ER)
  • Equine polysaccharide storage myopathy(PSSM)
  • Hyperkalemic periodic paralysis(HYPP)
  • Fibrotic myopathy
  • Inflammatory myopathy
  • Nutritional myopathy
  • Toxic myopathy
  • Atypical myopathy
  • Post anesthetic myopathy
  • Ischemic myopathy

Equine exertional rhabdomyolysis (ER) occurs due to abnormal Ca homeostasis within the muscle cells; causing muscle contraction to be intermittently disrupted, damaging the muscle tissue of the horse. The most common causes of this are excessive exercise and a high-grain diet.

Equine polysaccharide storage myopathy (PSSM) is a genetic disorder that occurs due to a dominantly inherited gene mutation.

Hyperkalemic periodic paralysis (HYPP) is another genetic condition that results from a point mutation in the Na channel gene in the skeletal muscle. When these abnormal Na channels are activated, they decrease Na-K exchange through the channel. This results in an increase in intracellular Na level and K level in the extracellular space, causing hyperkalemia. The most common cause of this myopathy is feed that is high in potassium, such as soya bean meal or oil, sugar molasses, beet molasses, alfalfa hay, brome hay, canola oil, grains such as corn, wheat, oats, and barley or beer pulp.

Fibrotic myopathy occurs when the inner thigh muscles are injured via exercise, trauma, or IM injection.

Inflammatory myopathy occurs via bacteria, viruses, and some parasites infecting the muscles.  Equine influenza 2 and Equine herpesvirus 1 are common viruses which cause this myopathy.
Sarcocystis fayeri, an infectious parasite, enters the horse via feed which is contaminated with canine feces.  Another infectious parasite, Anaplasma phagocytophilum, can enter a horse via a tick bite.

                       Bacteria such as Streptococcus equi equi and Clostridium spp. (C.septicum / C.perfringens/ C.chauvoei) can be a cause of inflammatory myopathy in horses. S.equi, Staphylococcus aureus, Corynebacterium pseudotuberculosis often cause muscle abscesses.

Nutritional myopathy in horses is associated with a deficiency of antioxidants like Selenium (Se) or vitamin E (Vit. E). A Vitamin E deficiency occurs when the horse eats low quality grass hay. This condition is common in foals up to 2 weeks old and young adult horses.

Toxic myopathy is caused by ingestion of poisonous portions (leaves/fruit/seeds) of certain plants like coyotillo (Karwinskia humboldtians), coffee sennas (Cassia occidentalis), white snakeroot (Eupatorium rugosum), and box elder seeds (Acer negundo). As well as certain plant toxins, ionophores are also toxic to horses. These are often used as a feed additive for poultry and other livestock, but should not be fed to horses. If a horse’s feed is accidentally contaminated with ionophores, toxic myopathy occurs. Horses are ten times more sensitive to ionophores than any other species.

Atypical myopathy is a fatal muscle disease caused by the ingestion of sycamore seeds, seedlings, and leaves.

Problems in the horse’s circulatory system cause post-anesthetic myopathy and ischemic myopathies.

How to treat muscle problems

As long as you get to the root cause of a horse’s muscle problems, treatment is easy. In mild cases, owners can manage these problems themselves, but in severe cases it is essential to seek help from a veterinarian.

Dehydration and electrolyte imbalance is the primary cause of most muscle disorders. Ionized Ca in the serum is an essential mineral which allows muscle contraction to take place. To prevent a hypo-calcemic condition, a sufficient amount of Ca, Mg, Na, K, and Cl, as well as essential minerals for healthy muscles should be provided as part of the horse’s diet. Changing the horse’s diet is a common treatment for several different muscle problems, however the exactt dietary change required varies according to the problem. A horse with nutritional myopathy, for instance, must be provided with sufficient dietary Se and Vitatim E.
          A diet containing fresh grasses is good for horses with HYPP as fresh grasses have a high water content, and eating them can also help to reduce K intake.

There are no antitoxins for muscle problems like atypical myopathy and toxic myopathy, however certain medications can help stop or reduce the absorption of toxins from the intestine.

Besides dietary changes, horses should be provided with freshwater or electrolyte supplemented water to help prevent dehydration. Anti-inflammatory drugs and antibiotics are the main treatments for inflammatory myopathy. Injectable methocarbamol, IV fluids and pain relievers can also be used to treat muscle disorders. If these treatments do not work sufficiently, surgery may be required.


Healthy muscles are essential for the wellbeing of a horse. Because horses are athletic animals, injuries and muscle disorders happen frequently. The common causes of these disorders are strenuous exercise, dehydration, electrolytic imbalance, intoxication, and genetic mutations. The best way to prevent these disorders is through providing sufficient dietary nutrients, however problems can often be treated with proper management and medication.

Degenerative Joint Disease in Horses

Equine Sports Massage Therapy

Introduction to Degenerative Joint Disease

Degenerative Joint Disease is a common condition in horses, also commonly known as osteoarthritis. This is a non-inflammatory form of arthritis which frequently occurs in synovial joints. A synovial joint is a moveable joint characterised by a fibrous capsule, articular cartilage, and a synovial fluid-filled cavity. The articular cartilage is hyaline cartilage that lines the epiphysis of the joint end of two bones. Articular cartilage helps to minimise friction while transmitting mechanical forces between two bones and increasing the joint’s contact surface area.  The joint capsule is a fibrous capsule which helps to cover all structures of the joint.

          Knees, hocks, and fetlocks are commonly affected by osteoarthritis. The condition can occur within a single joint or within multiple joints. Depending on the location, it can be either symptomatic or asymptomatic. The condition is common among horses of all ages, but it occurs most frequently in adult sporting horses. The causative agent for degenerative joint disease is still unknown, however stress occurring in the joints due to heavy workload, poor management, genetic problems, and poor practice methods can cause a predisposition to this condition.
        Degenerative changes in the articular cartilage are the leading cause of osteoarthritis. Horses which are able to carry heavy loads have thick articular cartilage. As the animal ages, the thickness of articular cartilage gradually decreases, and eventually the animal’s weight-bearing capacity also decreases.

Bone damage in the joints causes mild changes in the smooth surface of the articular cartilage in the epiphysis of bones. This leads to degenerative changes in articular cartilage, which is the major predisposing factor for degenerative joint disease.

Some breeds of horses are more susceptible to osteoarthritis, and have certain sites that are more prone to this condition. Osteoarthritis in the hock joint, for instance, is common among cutting horses, and osteoarthritis in the knee joint is common among racehorses.

What are the symptoms? How do I diagnose my horse’s pain?

As a horse owner, you should always identify symptoms of any condition as soon as possible in order to prevent these conditions from becoming more severe. If you fail to identify the early clinical signs of degenerative joint disease, the results can be profound. If you have identified early signs of osteoarthritis, you should commence treatment as soon as possible. It is always advisable to contact your veterinarian if symptoms appear.

Osteoarthritis is a progressive chronic disease, with clinical signs including lameness, stiffness, swelling of the affected area and pain. The most common clinical sign in affected horses is lameness. You can read our lameness article for a more detailed look at this condition and its symptoms. To give a basic run-down of the condition, lameness is defined as an abnormal gait or lack of capability to maintain a normal gait. Lameness is not a disease in itself, but is a clinical symptom of other conditions. Lameness usually results in pain and mechanical restriction of the horse’s limb. 

Another clinical symptom in horses suffering from osteoarthritis is stiffness. Animals suffering from this symptom are often reluctant to move and present restrictions in the motion of the affected limbs.
         Accumulation of fluid in the joint capsule causes swelling to the affected area. Changes in colour and increased temperature around the joint can also be indicators of degenerative joint disease.

When osteoarthritis is chronic, the articular cartilage is completely worn out. This means that there will be a lack of cartilage covering the edges of the two bones in the joint around the epiphysis. Free margins of the bones directly touch one other when the animal makes any movements, causing severe pain and discomfort to the animal, resulting in stiffness, lameness and restriction of movement.  If you attempt to exercise an animal suffering from this condition, it will likely display aggressive behaviours. It is important to identify the condition early and remove the animal from work to give it some relief.

Horses affected by this condition may also feel stress and may reduce their feed intake. This can result in the animal suffering from emaciation, weight loss, and lack of power and energy in performance. If you think your horse may be suffering from osteoarthritis, take immediate action. Contact your veterinarian, who will perform further diagnostic methods and start treatments. If you fail to take immediate action, your horse’s performance may be affected permanently. 

A number of confirmatory diagnostic methods such as X-rays, arthroscopy, nuclear scintigraphy, and serum biochemical tests can help to confirm if your animal is suffering from osteoarthritis. Arthroscopy is a new and very sensitive technique which identifies defects in the articular cartilages. Using this method, a clinician can obtain a clear image of the inside of a joint. This helps to diagnose osteoarthritis in its early stages. Although X-ray is commonly used as a confirmatory method, it is not able to identify changes in articular cartilage. It can, however, identify the narrowing of the joint space caused by the loss of articular cartilage.
      Nuclear scintigraphy is another very sensitive test. This is a method of bone scanning from which inflammatory joints can be identified. Serum biochemical testing is a biological technique which can also be used for the early diagnosis of joint disease. A biomarker is used as an indicator, which can give the clinician an idea of the metabolic processes inside a horse’s body. Changes in the specific serum enzymes (biomarkers) in the blood can indicate that a joint disease is present.

How to look after a horse with DJD?

Above all, it is important not to panic if your horse is diagnosed with osteoarthritis.  By managing the condition with great care, you can help to reduce the spread of disease within the horse and keep the animal comfortable. Do not use the affected animal for heavy workouts. Mild exercises, however, are recommended to maintain activity in the joints. Affected horses can tend to become overweight due to a lack of exercise, and it is important to do your best to avoid this happening. Providing sufficient shelter and good bedding will help the animal lie down and get up easily.

        Sadly, degenerative joint disease is incurable. Although it is not possible to cure the disease, it is possible to reduce its spreading, reduce the animal’s pain, and help to allow the articular cartilages to regrow. In order to achieve all of the above, try the following:

Trim the horse’s hooves properly to ensure its balance. Shoes should be fitted using proper methods as improper shoeing and unbalanced hooves predispose the animal to degenerative joint disease and make the condition more painful and severe.

Some of the easiest treatments to carry out are hot and cold therapies. Hot therapy can reduce pain and stiffness by increasing blood flow. This helps to relax the ligaments and tendons. Cold therapy helps to reduce the swelling and pain around the joint.

A healthy balanced diet can provide essential nutrients for joint repair. Some nutrients in the diet can even help to relieve pain. Proper nutrition will prevent your horse from becoming overweight, a condition which can incur further issues and symptoms.


You should now have a good knowledge of degenerative joint disease and its clinical signs, diagnostic methods, prevention methods, and treatment! To summarise, it is a degenerative disease affecting the articular cartilage. Also known as osteoarthritis, it is a complex condition which can result in gait abnormalities and pain. This can lead to a significant decrease in performance.  Do consider preventative action, and keep an eye out for any symptoms in your horse so that you can treat the disease promptly and effectively!