Equine Exertional Rhabdomyolysis (ER) or Tying Up or Azoturia or Monday Morning Disease is a syndrome that damages the muscle tissue in horses. It is usually due to overfeeding a horse carbohydrates.

Causes and Process of ER

There does not seem to be a single cause of ER in horses. Exercise is seen in every case, but exercise is always accompanied by another factor. It is likely that several factors must act together in order to cause an ER attack.

Other possible factors include:

• The overfeeding of carbohydrates (grain and pellets, for example)
• Poor conditioning or fitness, sudden increase of workload
• The work of a horse after a period of rest, if the grain diet was not reduced
• Electrolyte or mineral imbalances, especially seen with potassium
• A deficiency in selenium or vitamin E
• Imbalance of hormones, including the reproductive hormones in nervous fillies and mares and thyroid hormones in horses with hypothyroidism
• Heredity
• Wet, cold, or windy weather conditions

The more factors that are present, the greater the likelihood that the horse will develop ER. However, the most common cause of ER is an imbalance between the animal's diet and his workload, especially when he has a high-grain diet. General Name, Symbol, Number selenium, Se, 34 Chemical series nonmetals Group, Period, Block 16, 4, p Appearance gray, metallic luster Atomic mass 78. ... Tocopherol, or Vitamin E, is a fat-soluble vitamin in eight forms that is an important antioxidant. ... Hypothyroidism is the disease state caused by insufficient thyroid hormone by the thyroid gland. ...

ER occurs when there is an inadequate flow of blood to the muscles of an exercising horse. The muscle cells, lacking in oxygen, begin to function anaerobically to produce the needed ATP. The anaerobic work creates a buildup of waste products, acid, and heat. This subsequently alters the cell by preventing the cell's enzymes from functioning and the myofilaments from efficiently contracting. The cell membranes may then be damaged if the horse is forced to continue work, which allows muscle enzymes and myoglobin to leak into the bloodstream. Adenosine triphosphate (ATP) Adenosine triphosphate (ATP) is the nucleotide known in biochemistry as the molecular currency of intracellular energy transfer; that is, ATP is able to store and transport chemical energy within cells. ... Myoglobin 3D structure. ...

The body builds up a store of glycogen from converted carbohydrates in muscle cells. Glycogen, a fuel used by muscles for energy, is depleated during work and restocked when a horse rests. Oxygen-carrying blood metabolizes glycogen, but the blood can not flow fast enough to metabolise the excess stored glycogen. The glycogen that is not metabolized aerobically (by the oxygenated blood) must then be metabolized anaerobically, which then creates the cell waste products and heat, and ER has begun. A horse on a high-grain diet with little work collects more glycogen in its muscles than it can use efficiently when exercise begins, which is horses on a high-grain diet are more likely to develop ER. Glycogen is the principal storage form of glucose in animal cells. ... Aerobic is an adjective that means requiring air (where air usually means oxygen). ...

Proper conditioning can help prevent ER, as if promotes the growth of capillaries in muscles and the number of enzymes used for energy production in muscle cells. However, improvement in these areas can take several weeks. Thus, ER is more common in horses that are only worked sporadically or lightly, and in horses just beginning an exercise regimen. Capillaries are the smallest of a bodys blood vessels, measuring 5-10 μm. ...

A common misconception is that ER is caused by the buildup of lactic acid. Lactate is not a waste product for a cell, but a fuel, used when the cell's oxygen supply is insufficient. Lactate does not damage a cell, but is rather a byproduct of the true cause of cell damage: inadequate blood supply and altered cell function. Lactate naturally builds up in an exercising horse without harming the muscle cells, and is metabolized within an hour afterward. Lactic Acid Molecule Chemical and biological uses Lactic acid (α-hydroxypropionic acid) is a chemical compound that plays a role in several biochemical processes. ... Lactic acid is a chemical compound that plays a role in several biochemical processes. ...

The pain is caused by the inadequate blood flow to the muscle tissue, the inflammation from the resulting cell damage, and the release of cell contents. Muscle spasms, caused by the lack of blood to the muscle tissue, are also painful.

Symptoms of ER

A horse developing ER will usually begin showing signs right after the begining of exercise, although for mild cases, signs may not be seen until after the horse is cooled out. Signs include reluctance to move, stiffness or shortened gait when the animal if forced to move, and muscle spasms or cramps, with hard, painful muscles (especially the hindquarters) when palpated.

Usually there is a correlation between how long it takes the signs to be seen and how severe the bout of ER is, with the more severe bouts of ER displaying signs right after work has begun.

Signs of a severe bout of ER may include: sweating, elevated heart and respiratory rates as a result of the pain, anxious expression, shifting of weight from side to side, standing hunched and tense, passing redish brown urine, dehydration, shock, and inability to rise.

If signs of ER are seen, DO NOT MOVE THE HORSE. Movement can cause further muscle damage. If the animal is far from the barn, it is best to trailer him back than to move him.

After a bout of ER, blood levels of CPK and AST rise. CPK may refer to: Creatine kinase Cabbage Patch Kids California Pizza Kitchen This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... AST is a three-letter abbreviation that stands for a number of different things. ...

Treatment of ER

Mild or Moderate Cases

The horse should receive several days of NSAIDs, rest, and grain or pellets should be withheld. To improve blood flow to the muscles and help to with muscle spasms, heat therapy and massage may be beneficial, as well as hand-walking if the horse is comfortable walking. Turn-out in a pasture or paddock will encourage movement. A horse should be moving normally within 12-36 hours after the attack. Non-steroidal anti-inflammatory drugs, usually abbreviated to NSAIDs, are drugs with analgesic, antipyretic and anti-inflammatory effects - they reduce pain, fever and inflammation. ...

Severe Cases

A horse may need fluids, especially if his urine is colored, the horse is receiving NSAIDs, or if he is dehydrated. Fluids will increase the production of urine that will in turn help flush out the excess, and potentially damaging, myoglobin from the kidneys and will reduce NSAID-produced kidney damage. Fluids should be administered until the urine is clear, which usually takes from a few hours to a few days. Non-steroidal anti-inflammatory drugs, usually abbreviated to NSAIDs, are drugs with analgesic, antipyretic and anti-inflammatory effects - they reduce pain, fever and inflammation. ... Myoglobin 3D structure. ...

Vasodilators, such as acepromazine, can help improve blood flow to the muscles. However, the owner should only give ace if it is prescribed the horse's veterinarian, as it can lower the animal's blood pressure and can cause collapse in a severely dehydrated horse. The human drug dantrolene is sometimes given to alleviate the muscle spasms and prevent further degeneration of muscle tissue. A vasodilator is a substance that causes blood vessels in the body to become wider by relaxing the smooth muscle in the vessel wall. ...

Vitamin E is an anti-oxidant, and so may help prevent further cell degeneration in the affected muscles. However, vitamin E products must be used with caution if they also contain selenium. Tocopherol, or Vitamin E, is a fat-soluble vitamin in eight forms that is an important antioxidant. ... General Name, Symbol, Number selenium, Se, 34 Chemical series nonmetals Group, Period, Block 16, 4, p Appearance gray, metallic luster Atomic mass 78. ...

Bicarbonate will not help offset any lactic acid in the bloodstream, as lactic acid generally only accumulates in the affected muscles. A Bicarbonate or, more properly, a hydrogen carbonate is a polyatomic ion whose formula is HCO3-. It is the intermediate form in the deprotonation of carbonic acid: removing the first proton from carbonic acid forms bicarbonate; removing the second proton leads to the carbonate ion. ... Lactic Acid Molecule Chemical and biological uses Lactic acid (α-hydroxypropionic acid) is a chemical compound that plays a role in several biochemical processes. ...

Except to get a horse to his stall, a horse showing signs of severe ER should not be moved until he is comfortable enough to do so eagerly. This may take several days. After this point, it is important to either hand-walk the horse a few times each day, or to provide him with a few hours of turnout in a pasture or paddock.

Returning the Horse to Work

A horse may be returned to work after it is no longer showing signs of ER, and is no longer on NSAIDs--which can hide signs of another bout of ER. If NSAIDs are needed to keep the horse comfortable, or if the horse is reluctant to continue work, the animal is not yet ready for a return to his regular training program. Blood tests should reveal that the horse's CPK concentration and AST levels are normal before returning the horse back to work. Creatine Kinase Creatine kinase (CK), also known as phosphocreatine kinase or creatine phosphokinase (CPK) is an enzyme (EC 2. ... Aspartate transaminase (AST) also called Serum Glutamic Oxaloacetic Transaminase (SGOT) or aspartate aminotransferase (ASAT) (EC 2. ...

To begin bringing the horse back, he should be exercised at the walk and trot for 10-15 minutes at least once every day. This regimen will gradually be increased as the horse becomes more willing. For a moderate or severe bout of ER, this may take 4-6 weeks to return to the regular program. It is important not to push the horse more than he is ready or a relapse may occur. A second bout of ER is usually more severe than the first, not only taking the horse out of training for a longer time, but possibly causing permanent muscle damage.

Grain is gradually reintroduced as exercise resumes, but it is important to remember that grain can contribute to the development of ER.

Prognosis for ER

For mild to moderate cases of ER, the prognosis is excellent, with the horse successfully returning to its former level of competition. However, if the vet's recommendations for preventing ER are not followed, ER may likely reoccur.

Horses who experience a severe case of ER (the muscle degeneration is significant) are less likely to return to their previous level of competition, as fibrosis may have occurred which would result in loss of muscle function. The prognosis is guarded for these horses. Fibrosis is the formation or development of excess fibrous connective tissue in an organ or tissue as a reparative or reactive process, as opposed to formation of fibrous tissue as a normal constituent of an organ or tissue. ...

Prevention of ER

Diet

Reducing any extra energy in a horse's diet is essential to maintaining a horse that has experienced ER. Decreasing carbohydrates and increasing the daily intake of hay or pasture can usually accomplish this. Grain may need to be cut out altogether and replaced by a substitute, such as vegetable oil, to meet the individual energy needs of the horse.

Grain should be reduced or removed from a horse's ration on days when he cannot be worked.

Exercise

Proper conditioning is very important in preventing ER. Beginning with a base of long, slow distance work will ensure that the horse has a foundation before proceeding on to more strenuous work. The horse should always have a 10-minute warm-up at the walk and trot before more strenuous work is begun, and should always have a proper cool down of 10 minutes.

It is best that a horse receive exercise everyday, or possibly twice a day, to prevent the recurrence of ER. If possible, avoid breaks of the horse's exercise schedule. If for some reason the horse cannot receive training, he should at least be ridden, driven, longed, or turned out.

Daily pasture turnout is ideal for horses likely to suffer from ER, as it provides exercise and adds roughage to the animal's diet.

Supplements & Drugs As with any supplements and drugs, it is best to confer with your vet as to the recommended dosages. It is also important to remember that some drugs are not allowed in competition, and may need to be withheld a few days before.

Adding potassium and salt to the diet may be beneficial to horses that suffer from recurrent bouts of ER. Horses in hard training may need a vitamin E supplement, as their requirements are higher than horses in more moderate work. The horse may also be deficient in selenium, and need a feed in supplement. However, it is important to remember that selenium can be dangerous if overfed, so it is best to have a blood test to confirm that the horse is in need of supplemental selenium.

Thyroid hormone supplementation is often beneficial for horses with low thyroid activity (only do so if the horse has been diagnosed with hypothyroidism).

Other drugs that have been used with success include phenytoin, dantrolene, and dimetyl glycine.

Bicarbonate and NSAIDs are of no use in preventing ER.

Sources

King, Christine & Mansmann, Richard, VMD, PhD. Equine Lameness. Copyright Equine Research (1997). Pages 357-368.