Management of Chronic Exertional Rhabdomyolysis
Stephanie Valberg, DVM, PhD
Neuromuscular Diagnostics Lab
University of Minnesota, College of Veterinary Medicine
If the horse has suffered from stiffness within the last two weeks, or has just been diagnosed as having chronic ER, the first step is to turn the horse out for two weeks while implementing the recommended dietary changes. Once the horse has been on the diet for two to four weeks, round pen or light lunge line work (once a day for three minutes at a walk and trot) can begin. This initial work should be very mild and very short in duration. Gradually increase the time in work by two minutes each day, with a two minute walk break before the increased exercise. If the horse becomes stiff, stop exercise immediately.
If the horse seems tired, do not continue increasing the work load, but let the horse gradually become acclimated to the workload. When the horse can comfortably walk and trot for 30 minutes on a lunge line, you may start riding the horse at the same exercise intensity (30 minutes of combined walk trot). Gradually increase the time the horse is ridden using intervals of walk and trot and then work into walk, trot, and canter. Be sure to monitor the horse's level of exertion. Your patience will be rewarded.
Keeping an ER horse active is important. If the horse cannot be ridden for several days, make sure that the horse is turned out as much as possible each day. A simple 10 minutes of work in a round pen or on a lunge line is very beneficial during the days the horse is not ridden. After more than 4 days out of work, the horse must be brought back up to normal exercise in a gradual fashion.
More than eight hours of inactivity (other than normal sleep/rest) should be avoided. This includes stall rest, trailering for long distances, and other forms of inactivity. If trailering for several hours, plan on unloading and hand walking for about 10 minutes every few hours. Horses should be turned out daily (for as long as possible) to promote constant movement. Larger pastures that encourage horses to move about to graze are best (see diet notes below regarding grass quality).
If the horse is highly excitable, acepromazine 1 cc in the muscle or 2 cc orally, 30 minutes before exercise may be an alternative when combined with the above diet and exercise program. Adjust the dose as needed to find a minimum amount the horse requires. Of course, this approach is not appropriate for racing.
Dantrolene (4 mg/kg) given orally. This medication decreases intracellular calcium release and may be very beneficial, yet expensive, in bringing horses back into training. It is best used if horses are not fed their morning meal, given dantrolene on an empty stomach and exercised 1 hour after medication orally. This medication is not absorbed if horses are fed prior to medication and its peak effect is 90 min after administration. Horses cannot race on this medication. It should be gradually withdrawn once horses have settled into a training regime.
It is important to reduce the sugar or starch in the diet both in forage and concentrates and replace these calories with a fat supplement. Feeding high quality grass hay with little to no alfalfa will decrease the starch in the diet. Rich grass pastures with lush growth are not recommended.
Feeds should provide less than 20% of daily calories as nonstructural carbohydrates (NSC) and preferably less than 15% of daily calories as NSC for difficult cases. Many fat-supplemented feeds currently on the market are also high in starch, which will induce tying-up, so careful choice of feeds is necessary.
No improvement will occur if a high starch, high fat supplemented feed is substituted. If buying a commercial high fat feed, consult with the company's representative on how much starch is in the product. This information will not be found in the analysis table on the feed bag. Specifically inquire about nonstructural carbohydrates and the balance between carbohydrates and fat in any commercial feed formula. A list of some potential complete high fat, low starch diets is provided.
Forage: A high-quality grass or oat hay should form the basis of the diet. If alfalfa hay must be fed, a mixture (half alfalfa and half oat hay) may be the best option. Vitamin and mineral supplements containing Vitamin E and selenium are beneficial; however, some feeds (including some recommended below) contain enough selenium and other vitamins and minerals and do not require additional supplements. Check with the feed company if there are any questions. We have found that these dietary changes can have a beneficial calming effect on horses.
Complete Feeds: these feeds do not require additional protein/vitamin/mineral supplements and are to be fed along with hay. No additional grain or mineral/vitamin mix should be added. Re-Leve®** by Hallway Feeds (www.Re-Ieve.com, Phone 1-800-753-4255) was developed with University of Minnesota researchers, has been proven to be effective for RER and is good for finicky eaters. Starch content is low (9.0% by weight) and fat content high (12.5% by weight). Additional selenium should not be fed. 3-5 lbs fed for light to moderate work 6- 10 lbs for thin horses or horses in heavy work For overweight horses, reduce hay to 1% of body weight and still feed Re-leve
Other Complete feeds may be available in your area that can be fed with grass hay: Ultium® by Purina in the USA:10-14 lbs per day. www.purinamills.com. or 800-227-8941 XTN® at 5-8 lbs per day combined with Empower® at 3 lbs/day by Nutrena. www.nutrenaworld.com. Other options require that you speak to the nutritionist at the company and that they design a diet that meets the nutritional requirements provided in Table 1. In general, the starch content of the feed should not be greater than 15-20% by weight and the fat should be greater than 10% by wt.
Blending of individual feeds: Fat supplements combined with additional protein1 vitamin/mineral mixes and a fiber base can be custom blended. If these feeds contain more than about 3 Ibs of grain per day or the equivalent amount of starch they often induce tying-up in susceptible horses. Consult with the manufacturer's nutritionists to formulate the correct blend for a horse with ER which is specific to breed and level of use
Fat supplements containing stabilized rice bran: EquiJewel® Kentucky Equine Research, Phone (859)873 1988, Fax (859)873 3781, Email firstname.lastname@example.org. ker.com/supplements/Equijewel.htmI Natural GIo® (rice bran) Alliance Nutrition. Phone 1-800-680-8254 email AN.EquineHelp@adm.corn, website www.admani.com/horse Ultimate Finish® by Buckeye Nutrition, PO Box 505, 330 E. Schultz Ave. Dalton, OH 44618. Phone: 1-800-898-9467 Fax: (330) 828-2309, www.buckeyenutrition.com/equine
Vegetable Oils: Corn oil or soy oil gradually can be added at 1-2 cups per day to a fiber base such as hay cubes or alfalfa pellets or feeds such as Purina Horse Chow. Add 600 U of vitamin E/cup of oil per day.
Electrolyte balance: Ensure that salt is always available. If horses will not use a salt block, add 1-3 tablespoon of loose iodized table salt in the feed, particularly in hot weather. If the horse is sweating a great deal, an additional tablespoon of lite salt (containing potassium chloride) can be added.