Tying Up? What you Must Know

Tying-up has many names and can be called exertional rhabdomyolysis (rhabdomyolysis means destruction of skeletal muscle cells), azoturia, set fast, Monday morning disease, or paralytic myoglobinuria. This last name is due to some horses passing dark red urine some horses produced due to a red protein called myoglobin that is released from damaged muscle cells and excreted in the horses urine.

Tying Up can Cripple your Horses Performance

Horses which are often described as tying up commonly used to describe horses that are stiff, sweaty, and reluctant to move due to pain originating from the large muscle groups in the back, pelvis, and hind limbs. In some severe cases, the muscle in the forelimbs and the shoulders can also be affected.  Mild cases of tying-up can be challenging to diagnose because the horse might only seem stiff, "off," or slightly lame. Horses who suffer moderate to severe tying-up episode show not only the classic signs described above, but can also exhibit an elevated heart and respiratory rates and appear anxious or colicky. These symptoms are a sign of the horse being in pain.  In infrequent cases, severely affected horses can have massive muscle damage which can lead to kidney failure and even death.

So What are the Causes of Tying-Up?

TB Fillies Prone to Stress are Prone to Tying Up

Horses can tie up either unexpectedly/sporadically or chronically, ongoing, and be a frustrating problem. Possible reasons for a horse sporadically tying-up includes exercising beyond the current level of conditioning; sudden changes in training regimens; exercising in hot, humid conditions; a recent history of a viral respiratory tract infection; gender (high-strung/nervous fillies and mares appear to tie up more frequently than males); and finally dietary issues. 

A typical case study of a horse prone to tying up would be a nervous filly fed a high-grain diet which is not balanced and is lacking selenium/vitamin E, electrolytes, and/or minerals.  This filly might tie up more frequently than horses with balanced diets. Tying-up in some Thoroughbred racehorses is thought to be caused by abnormal regulation of muscle contraction.

Specifically, horses affected with tying up appear to have a defect in how the calcium is pumped back and forth into storage sites within muscle cells, which can lead to muscle cramping and damage.  Calcium is a crucial part of the process which maked muscles contract.   In these horses, stress, excitement, lameness, high-grain diets, and certain levels of exercise are thought to be potential factors that trigger this abnormal calcium regulation.

Quarter Horses and draft related breeds can experience recurrent or chronic tying-up can be due to the horses muscles storing too much glycogen (sugars) in the muscles. 

Diagnosis

You will need to get your vet to make a diagnosis of tying up.  It will usually be made based on a physical examination and blood work, including measurement of muscle-specific enzymes in the blood serum sample. Creatine kinase (CK) levels can reach extremely high levels beginning within hours of the horse tying-up, whereas other enzymes- such as lactate dehydrogenase (LDH) and aspartate amino transferase (AST)-are longer-term indicators of tying-up. These enzyme levels peak approximately 12 and 24 hours, respectively, after the damage has occurred. CK levels return to normal within three to seven days; other enzyme levels can take up to 14 days to return to normal. Monitoring enzyme levels can help establish a diagnosis and be used to guide the owner, trainer, and veterinarian in determining when it is appropriate to return the horse to exercise. Establishing that a horse has in fact tied up is relatively easy, finding out the underlying cause of the tying-up episode can be much more of a challenge and generally requires trialling dietary and exercised changes. You may require additional diagnostic tests, such as muscle biopsy.

Like any disease, it is essential to be sure of the diagnosis.  With anything reoccurring it is easy to put every issue down to that problem and exclude looking for other reasons.  Tying up can be confused with more serious musculoskeletal conditions such as a fracture, laminitis, or conditions such as neurological diseases. Signs associated with the accidental ingestion of poisonous plants or other toxins can also be mistaken for tying-up.

Treatment

A Symptom of Tying Up is Strong Dark Urine

If you suspect your horse is tying-up, immediately stop exercising the horse and place him/her in a yard of stable and call your vet. While waiting for the vet, do not move the horse, try and keep them calm and still. Place a blanket on your horse if the weather is cool and offer small, frequent amounts of water. You can also offer a salt block or a bucket of water with electrolytes added to it. Offer hay only until directed otherwise by your vet.

Since there are multiple causes of tyingup, there is no one single treatment plan. Your vet will treat the horse depending on the severity and underlying cause (if known), they could possibly give a sedative such as Acepromazine and an anti-inflammatory such as phenylbutazone to help control pain and to relieve anxiety.

Some vet might also choose to administer intravenous fluids.

Recovery

Most horses recover within a few days, however severe cases can take onwards from 10 days or more. Once the horse is pain free and begins to move again, you can turn them out in a small paddock. When the enzyme levels are at or near normal limits, activity can be slowly reintroduced in a very controlled and careful fashion.

Some horses with chronic tying-up are kept active even when their muscle enzyme levels are above normal as total rest seems to exacerbate signs of muscle stiffness, however you will need to work closely with your vet on this.

Prevention

Your vet will recommend specific preventive strategies based on the cause of your horse's tying-up, but there are some general ways to help prevent episodes. For example, maintain a regular exercise regime and increase training gradually, not abruptly. In young, high-strung fillies, establish a daily routine, minimize stress, and modify her diet to include a balanced vitamin and mineral supplement, feed high-quality hay with minimal grain and sweet feed, and increase the amount of fat fed (in the form of vegetable oil, for example  Ranvet's Racing Oil). These dietary changes can be appropriate for other horses suffering from chronic or recurrent tying-up. Acepromazine can be used daily at low doses in stressed or nervous horses that tie up frequently, and dantrolene can be fed to fasted horses one hour prior to exercise to potentially prevent an episode. Daily oral administration of phenytoin has been advocated, but can cause drowsiness depending on the dose. Each of these options requires a prescription from your vet - so work closely with them to work things through.

Remember to plan means nothing, but planning means everything - so you will need to work with your vet to create a plan to manage your horses exercise and nutrition for the good of all!  Best of luck!

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