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The Tying Up Syndrome

The term exertional rhabdomyolysis is the scientific description for tying-up, and simple means muscle cell death from exertion. First identified in the late 18o0’s as Monday Morning Sickness or azoturia, it was observed in working horses given the weekend off, confined in stalls and fed their full grain ration. When brought out to work on Monday morning, affected horses would suffer severe muscle cramping, profuse sweating, rapid breathing, and possibly pass dark reddish-brown urine.


We now know that horses tie-up for a number of different reasons, including dietary electrolyte imbalance, high body temperature, unusually intense exercise or stress. These situations occur in otherwise normal horses and are remedied by correcting the electrolyte balance in the diet or maintaining a more consistent exercise program and avoiding highly stressful situations. Other horses have a muscle disorder, Polysaccharide Storage Myopathy (EPSM or PSSM), which makes them more prone to tie-up. EPSM is found in all breeds, but appears more prevalent in Quarter Horses, Arabians, draft breeds and Warmbloods. It has been documented in horses from 3 months to 29 years of age.


Tying-up is the most obvious symptom of EPSM but there may be many more subtle symptoms. Horses with EPSM may show a lack of energy, decreased performance, back soreness, abnormal hind leg movement, stiff gait, loss of muscle over the topline and hindquarters, muscle tremors following exercise, episodic colic and/or general irritability and bad attitudes while being groomed, saddled and ridden. Symptoms can suddenly appear in a horse that has never tied-up before.


The underlying cause for EPSM is a defect in muscle metabolism and how these horses store an utilize energy in the muscles. They often respond well to therapy, including diet changes and regular exercise. Response to therapy is a good indication of the disorder, but a muscle biopsy provides the more definitive diagnosis. A complete veterinary exam is recommended to differentiate between EPSM and other conditions with similar symptoms.


Diet changes for EPSM horses involve adjusting the caloric sources in the diet. Typical diets of oats and other grain mixes provide calories primarily from starch and sugar, but EPSM horses may benefit from diets that provide more calories from fats and fewer calories from starch and sugar. There does not appear to be a one-size-fits-all diet, since horses with EPSM can have variations in starch/sugar sensitivity and the level of fat needed to help alleviate symptoms. Finding the diet that best manages an individual horse may take some trial and error.


For horses suspected of having EPSM, changing from a grain or grain mix to a pelleted feed with lower starch and added fat is the initial step. Horses seem to have an individual tolerance level for fat in the diet and, as fat is increased, some horses may back off feed. Therefore, small, gradual adjustments may be necessary. Higher fat, lower starch feeds such as Purina Ultium make these diet changes easier because the fat is already included in a palatable, nutritionally balanced pellet. When you add oil to existing feeds, additional supplements may be needed because increasing fat typically reduces total intake and increases the requirements for nutrients.


Some researchers recommend total fat intake up to 1 lb. of fat for 1000 lb horse, and reducing starch and sugar as much as possible. To calculate total fat intake, multiply the percent fat in the product times the amount fed. For example: 8 lbs of Ultium with 12.4% fat provides 8X0.123=1 lb of fat. There are also good fat supplements such as Purina Amplify which has 30% fat, so 3.3 lbs provides a pound of fat. One pound of fat could be provided by 2 cups of vegetable oil or 5 pounds of rice bran, but these fat sources do not provide balanced nutrients, so the total balance of the ration might be compromised and require adjustment.


After changing to a higher fat, lower starch diet, it may take four months to see significant changes in a horse with EPSM. However, if there is any improvement in symptoms during this period it is likely the horse will continue to respond well if maintained on the new diet. Some horses show an increase in energy level, sometimes to the point of “bouncing off the walls” during the first few months of diet change. This may be due to changing the metabolism of muscles to burn fat, and finally delivering energy to previously energy-starved tissues. These horse generally settle down after they adapt, and show improvement of EPSM symptoms on the new diet.


In addition to diet therapy, horses with EPSM are best managed by providing regular exercise and plenty of turnout time. It is important that they not be stalled for days without exercise. If they must be stalled without exercise, reduce their grain intake or eliminate grain altogether and instead feed a low starch concentrated protein, vitamin and mineral supplement, such as Nature’s Essentials Enrich 12 or Enrich 32. Horses with EPSM will always have the disorder, but adjustments in diet and management may help them continue to perform at very high levels.


The goal in all of these is to reduce starch and sugar and increase fat, which can be tough due to some of them not working hard enough to eat many calories.


Some of the programs we have that will work include:


1) Ultium

2) Enrich 32 + Amplify (horses with lower calorie needs)

3) Enrich 32 + Horse Chow + oil (for horses with higher fat needs, Horse Chow soaks up oil well, but not real high calorie requirements, Horse Chow can replace part of the hay)

4) Equine Senior + 1-2 pounds of Amplify or 1-3 cups of oil.

5) Strategy + 1-2 pounds of Amplify or 1-3 cups of oil.

6) WellSolve L/S + 1-2 pounds of Amplify or 1-3 cups of oil.


It will take a trial and error to find the program that works to manage each horse, as there is no “one size fits all” diet. Keep in mind, we can only offer to help better manage these horses, which means we can help reduce the incidence and the severity of the symptoms (tying-up episodes) but the horse has a condition that they will always have; it cannot be cured with feed alone.


Source: Tina Anderson, PhD, Equine Specialist, Land O’Lakes, Inc.