Tying up can be common in horses of various breeds. The exact cause is still unknown, but here is some information that can help you manage the muscle disorder.
“Tying-up” is one of the more common muscle disorders found in horses. In fact, we now know that there are several forms of tying-up and that RER or recurrent exertional rhabdomyolysis is just one of them (another one is PSSM, but more on that in another article).
Horses suffering from RER are unable to properly regulate the calcium ions that control normal muscle contraction and relaxation. When a horse has an episode of RER, the gluteal muscles “tie-up” or become hard. The horse becomes stiff and movement becomes painful. Horses often refuse to walk and will sweat profusely. The exact causes of RER are unclear and still under investigation, but what is understood thus far is that dietary deficiencies, exercise, high grain diets and/or excitement triggers the problem.
Horses suffering from RER are generally racehorses or event horses and can be a variety of breeds, including Thoroughbred, Arabian, or Standardbred. Research at the University of Minnesota Equine Center has revealed that horses may inherit a predisposition to RER; however, the condition may not become obvious unless the horse is exposed to the appropriate stress factors. Measuring protein levels in the blood and looking at muscle biopsies are some of the tools used to diagnose RER. The results of these tests coupled with a history of tying-up and other clinical findings confirm the presence of the disorder.
Managing horses suffering from muscle disorders requires simple but thoughtful changes to their daily nutrition. Good quality fiber should be the basis of the diet. Horses struggling with RER do better on grass or oat hay. If alfalfa is fed then it should be mixed with grass or oat hay. Feeding grains and feedstuffs high in sugar or starch can lead to a spike in blood glucose that triggers excitability and nervous activity in many horses. Fat supplements like rice bran and fermentable fiber such as beet pulp provide a source of low starch/sugar energy. Therefore, offering RER horses feeds that minimize the glucose spike and reduce the degree of excitability may prevent or decrease the occurrences of tying-up and muscle damage.
Additional vitamin E and selenium are beneficial to the RER horse; however, selenium can be toxic if overfed. Most commercial feeds and vitamin/mineral supplements already contain some selenium. It is vital that you know how much selenium is in your horse’s current diet before you add more. Work with your veterinarian or nutritionist to determine the appropriate selenium level for your horse and adjust his/her diet accordingly.
On the other hand, vitamin E can be fed at levels as high as 10,000 IU per day for horses suffering from neurological and muscular diseases. Nutritionists recommend 3,000 IU to 5,000 IU of natural vitamin E be provided daily to hardworking horses. When muscle issues arise the levels prescribed by your veterinarian can be higher. Hay and other dried fiber sources do not contain much vitamin E. Commercial feeds might provide some vitamin E, but typically only maintenance amounts or less. Supplements contain varying levels of vitamin E and some may mix vitamin E with other vitamins or minerals. When feeding vitamin E levels above maintenance (1,000 IU to 2,000 IU per day) it is probably best to pick a plain natural vitamin E supplement. This reduces the risk of over-feeding other nutrients that might be found in a “combo” supplement.
If the feed or supplement you use contains vitamin E make sure it is “natural vitamin E” (listed as d-alpha-tocopherol or natural vitamin E) not synthetic vitamin E (listed as dl-alpha-tocopherol or vitamin E supplement). Synthetic vitamin E is petroleum-based and not readily absorbed by the horse, while natural vitamin E is plant-based and more easily absorbed and retained in the tissues. Work with your veterinarian to determine the level of vitamin E needed to suit your horse’s situation.
RER horses should always have free-choice access to a block salt, or you can provide 1 to 3 tablespoons of iodized salt per day in the feed. When your horse is working hard enough to sweat, a balanced electrolyte should be provided. As with all horses, a continuous supply of fresh, clean water is essential.
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