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Tying Up in Horses

28/08/2017 by Tania Cubitt, PhD, Hygain Feeds, www.hygain.com.au

Exertional Rhabdomyolysis, Tying Up, Azoturia, Monday Morning Sickness and Poly Saccharide Storage Myopathy are all names of common muscle metabolism problems. 

The scientific name for tying up is rhabdomyolysis, which simply translated means muscle (‘rhabdo’) breakdown (‘lysis’). The causes are several, but the result is the same - muscle cramping. 

In this condition, there is massive contraction of the muscle groups along the back and rump of the horse. The muscles contract and do not relax. The horse will appear to be nailed to the floor in the back end, while seemingly being able to move the front end without any problems. They will appear to be in significant pain. 

When you press your hands along the muscles on either side of the spine, they feel rock hard. The horse’s temperature may elevate up to 40 or 40.5oC. 

If the cramping is severe enough, then the myoglobin released from the damaged muscle goes from the blood to the kidneys and into the urine, turning the urine dark red. Eventually, this may cause severe kidney problems. Most cases of tying up are not that severe, and usually present in a horse that has been off for several days and is then exercised aggressively. In the middle of the ride (or sometimes right at the end), the horse’s stride shortens and they cramp up.

Muscle disorders are a frequent cause of poor performance in horses and tying up is the most common syndrome. It is often mistakenly assumed any horse with muscle pain or cramping after exercise has ‘tied-up’.

Because of this, there is much confusion and controversy around the diagnosis, causes and management of affected horses. However, although a number of different muscle conditions produce the same signs, there are basically two types of tying up - acute and chronic.

Signs of tying up

The signs of tying up vary with the severity of the condition and the speed of onset. In mild cases, the horse’s gait gradually stiffens and they become reluctant to move. The muscles are actually cramping and feel very much to the horse like muscle cramps do to human athletes. The large, heavy muscles of the hind legs are most often affected, but the triceps above the elbow of the front legs may also be stiff and painful.

The horse often begins sweating profusely, and their heart and respiratory rates may also increase dramatically. The affected horse may appear to be colicing, but the major difference is in horses that are tying up, the large muscle of the hind legs will be firm or very hard, and the horse will paw the ground or attempt to lie down.

In extreme cases of tying up, the large muscles of the hind legs may actually appear to bulge. If there is enough muscle damage, the horse’s urine will turn a dark, reddish-brown colour as the damaged muscle fibres release myoglobin, which then passes in the urine.

Horses that tie up usually have a recurring problem, associated with a specific set of circumstances. When horses worked for a living, a common problem was ‘Monday morning disease’. This problem occurred when horses, which were working all week, did not have their grain cut back while resting over the weekend. Some horses tie up when they become excited, at a show, breeding or travelling. Other horses develop the problem when exercised. Occasionally, you run into the horse that ties up for no reason you can detect.

Moderate to severe cases are not hard to diagnose. The stiffness in the rear limbs and hard, painful muscles are easily seen. But, mild cases may present as decreased performance or a vague lameness originating in the back or hind end. In cases of possible tying up, the diagnosis can be confirmed with blood tests for increase levels of muscle enzymes.

Causes of tying up

A horse that is prone to tying up can be sensitive to several different things. It may not be feasible or necessary to fix them all. Learn what factors trigger an attack in your horse and work to minimise those. Work with training, spelling, feed and environmental stress. Keep a diary to look for patterns.

There have been several proposed causes for tying up. The different histories and varying treatments that horses respond to strongly suggest we are looking at several different diseases. Some proposed causes are:

  • Altered carbohydrate metabolism - recent work has identified abnormal carbohydrate metabolism as a cause in many breeds of tying up.
  • Hypotension/nervousness.
  • Electrolyte imbalances - horses which tie up during or following exercise frequently have electrolyte imbalances.
  • Mineral deficiency.
  • Lactate build up.
  • Too little oxygen getting to the muscles.
  • Vitamin E\selenium deficiency.
  • Hypothyroidism.
  • Hormone imbalances.
  • Dehydration.
  • Imbalanced mineral ratios in the diet.
  • Over-exertion in training.
  • Dramatic changes in training.
  • Genetic inheritance.

Types of tying up

Based on our current knowledge, horses which experience episodes of tying up can be placed in one of two broad categories:

Sporadic (acute) exertional rhabdomyolysis – this classification applies to horses which, on rare occasions, experience an episode of generalised tying-up. This will generally involve muscle stiffness and cramps.

Chronic exertional rhabdomyolysis – when a horse experiences repeated episodes of ER, with the first episode usually occurring at a young age. This can be quite a problem and may eventually, over repeated bouts of tying up, cause irreversible muscle damage.

Management of tying up

Diet and exercise are closely linked to tying up, and the most important preventative strategies are based upon diet and exercise management. The classic case is the horse fed high grain and then given a day of rest, hence the name ‘Monday morning disease’.

Dietary management 

  • A minimum level of grain - high cereal grain diets can overload the normal digestive processes of the small intestine, so the caecum and colon of the large intestine are flooded with undigested and semi-digested grains. Undigested nutrients reaching the large intestine are fermented, which results in increased lactic acid production, fluctuations in blood glucose and hormone levels, and increased heat of digestion, which the horse must sweat to cool - increasing fluid and electrolyte losses.
  • Balanced vitamin and mineral levels, especially vitamin E and selenium.
  • The correct amounts and ratios of the different electrolytes.
  • A high percentage of oil. Oils provide slow release energy and maintain steady blood glucose levels. Blood lactate levels are lower in horses on high oil diets
  • Good quality hay.
  • Supplements to reduce nervousness/stress, such as thiamine, magnesium and chromium.

HYGAIN® RELEASE® is specifically formulated for high performance horses prone to tying-up. HYGAIN® RELEASE® is designed to be low in starch (carbohydrates), high in fat and provided with more roughage than is usually fed to performance horses. HYGAIN® RELEASE® is also high in vitamins E and C, selenium, magnesium and calcium. 

Lower starch alternatives for equestrian horses in training and competition include HYGAIN® SHOWTORQUE®, a high fat, cereal grain-free feed for horses in moderate work, and HYGAIN® ICE®, a low starch, high fibre pellet for horses in light work, which provides slow release energy for both performance and overall body conditioning. 

It is imperative when you are using an electrolyte that is balanced, which means feeding your horse the same levels of electrolytes that are lost. HYGAIN® REGAIN® is an excellent electrolyte supplement, formulated to replace body salts lost during exercise, hot climatic conditions and as an aid in the treatment of dehydration, hypochloraemia and alkalosis, resulting from electrolyte loss.

When grains are processed, such as micronised or extruded, the starch is rapidly digested in the small intestine, which reduces the burden on the large intestine. An over burden on the large intestine can result in problems, such as colic, laminitis and tying up. All grains used in HYGAIN® feeds are either micronised or extruded. 

Exercise schedule

This will vary between horses, according to fitness, metabolic rate and individual variation, but several basic principles appear to be beneficial, including:

  • A consistent, structured program with no rest days.
  • Grading the level of exercise with a slow increase in intensity as fitness develops.
  • Hard work should be followed with a slow trot or canter to stimulate the delivery of oxygen to the muscles, and the removal of lactic acid from the muscles to the liver.
  • Adequate warming up and cooling down of the horse.

Management practices

Avoid stress and excitement - it is desirable to reduce fizzy, restless behaviour, especially in highly excitable horses. The ‘heating’ effect of cereal grains results from rapid fermentation in the caecum, producing abrupt rises in blood glucose and energy levels. Rapid changes in blood glucose levels cause fluctuations in insulin, cortisol and thyroid hormones, stimulating metabolic rate and restless behaviour. Processed grain, such as micronising, does not have the same effects as unprocessed grains.

Feed more often - stabled horses may become bored, nibbling and chewing wood, stable fittings and bedding. Frequent smaller feeds prolong chewing time, reducing boredom.

Medication may be required in some horses, and the particular therapy prescribed is based on clinical and laboratory investigations.

Veterinary treatment

A mild case of tying up may be treated with a nonsteroidal anti-inflammatory (i.e. Phenylbutazone) and rest for 3-5 days, with a gradual increase in exercise. 

Sedatives, such as Acepromazine, which cause sedation and relaxation by depressing the central nervous system may be given to decrease the anxiety and spasms after the horse ties up. In some chronic cases, Acepromazine may be used in a preventative effort prior to exercise to help promote vasodilatation - or opening of the outlying blood vessels. 

Veterinarians may give the horses immediate intravenous thiamine, or intramuscular vitamin E and selenium injections to aid return to health, or monthly prophylactic injections to decrease potential onset of tying up.

Horses exhibiting severe symptoms of tying up may be treated with intravenous fluids to decrease potential kidney damage, due to the myoglobin excretion and shock. Nonsteroidal anti-inflammatory drugs and/or painkillers may be necessary during recovery time. As with mild cases, a sedative may be used to decrease the anxiety and help prevent thrashing or excess movement. In severe cases, it is critical to limit movement to decrease potential permanent muscle damage. Recovery time may be up to 6-8 weeks and ability to return to work will vary with severity.

Horses that suffer from chronic attacks of tying up can often be managed successfully with strict exercise, management and diet protocols. Management strategies that reduce stressful situations, and provide a consistent and calm environment may help as well. Some horses may need to be maintained on sedatives prior to exercise, or given daily medication to decrease or prevent muscle damage during episodes.

Basic checklist for tying up

  • Stop exercising the horse and move it to a box stall.
  • Call your veterinarian.
  • Rug the horse if weather is cool.
  • Determine if the horse is dehydrated due to excessive sweating. 
  • Provide fluids - small frequent sips of water. Electrolytes (potassium, sodium, and chloride) may be added to drinking water, if palatable to the horse. Plain water should always be available as an alternative. 
  • Relieve anxiety and pain. Drugs may be prescribed by your veterinarian.
  • Remove grain and feed, and provide only hay until signs subside.
  • Hand walking or small paddock turnout is good once the horse walks freely, usually within 12-24 hours.
  • When blood creatine kinase (blood enzyme) is normal, slowly recondition the horse to the previous work level.
  • If the problem reoccurs, have the horse evaluated for a specific cause of recurrent exertional rhabdomyolysis.

Consider changing the diet, feed less grain and more fat, and make sure the mineral intake is balanced. Elevated levels of vitamins E and C, selenium and magnesium may also be useful (consult a qualified equine nutritionist).

While the chemistry of tying up is understood, the factors contributing to it are not as clear. Besides consuming too much unprocessed grain for their activity level, horses may also tie up as a result of dehydration, glucose depletion, electrolyte imbalances, mineral and vitamin deficiencies, over exertion, nervousness and hormonal fluctuation.

Due to the multiple causes of this condition, it is important to have a thorough veterinary examination to determine which factors are involved for each horse, so an accurate treatment and management plan can be developed. The examination may include blood and urine tests, muscle biopsies and an exercise challenge test.

One final point deserves emphasis. There is no cure for horses with chronic forms of tying-up, such as RER and PSSM. These conditions have also been shown to be inherited in some bloodlines.

The key to combat these disorders is vigilant management of your horse. With the correct management of nutrition and exercise, the chances of your horse tying up should be reduced.