Tying-up is the common term used to described exertional rhabdomyolysis, which is skeletal muscle damage related to exercise.
You’ll see the first symptoms of tying-up while the horse is working, although it may become more obvious when you slow down or stop. The horse will become reluctant to keep moving, sweat and start to breathe heavily. The sweating and breathing problems are due to pain.
Before you stop, or the horse flat-out refuses to continue working, the gait becomes rough and stilted. Once pulled up, the muscles, especially the hindquarters, will feel nearly rock hard. The horse will be extremely reluctant to move. In fact, because his muscles are in spasm, he will have a great deal of difficulty moving. It’s both painful and likely to cause more damage to the horse.
The horse may stand stretched out, like a horse with acute laminitis or colic. When he first passes urine after tying-up, it may be darker in color than normal, or start appearing normal then change to reddish or dark brown. The darker the urine, the more severe the muscle damage, although very dehydrated horses also have dark urine.
It’s important to cover the horse with a sheet or cooler of a weight appropriate to the weather. If you’re close to the barn, you can attempt to slowly walk the horse to his stall. If not, the horse should be trailered home.
Call your veterinarian immediately. Severe muscle damage releases myoglobin from the muscle, which can precipitate out in the kidneys and cause kidney damage. The horse needs treatment to relieve the pain and spasm and may need intravenous fluids to help flush and protect the kidneys.
Vets vary somewhat in their standard approach to tying-up, but among the treatments used for acute episodes are mild tranquilizers such as acepromazine, anti-inflammatory drugs or more potent pain relievers, benzodiazepines like Valium or muscle relaxants such as Robaxin, intravenous calcium and/or magnesium and intravenous fluids, sometimes with a diuretic. Oral branched-chain amino acids (BCAA: lysine, leucine, isoleucine) can help prevent excessive loss of muscle mass after a tying-up episode.
Horses that tie up generally fall into one of two categories: ones that have sporadic/isolated episodes and those that have repeated episodes. Horses that have no prior history of tying-up, or a remote history of having done it some time in the past, may have some degree of genetic predisposition to doing this, but there are usually management/dietary factors that come into play to push them over the edge. See our sidebar for common causes of tying-up.
The symptoms of tying-up are usually characteristic enough that it’s not a difficult diagnosis to make. Nevertheless, there have been instances where colic, acute back pain, even bilateral coffin bone fractures have been misdiagnosed as tying-up. In all those cases, persistence of the symptoms beyond the usual few hours it typically takes for spasms to resolve, or the failure to respond to tying-up-specific treatments, should raise the red flag that you might not be dealing with tying-up.
Even with a clear diagnosis, it’s wise to have blood work done to determine the degree of muscle damage. Monitoring blood work is also the ideal way to determine when exercise can resume. If enzymes don’t really normalize with avoidance of work, or it’s found that low-level work produces abnormally high muscle enzymes, the horse probably has recurrent extertional rhabdomyolysis (RER) or equine polysaccharide storage myopathy (known as PSSM).
Horses whose enzymes return to normal but experience tying-up again despite best efforts to control external factors are also likely recurrent tying-up cases of RER or PSSM. Horses that aren’t showing dramatic signs of tying-up but are suspected to have a muscle disorder on the basis of more subtle signs like muscular twitching or stiff gait, should be biopsied first before making major changes.
Vitamin E and Selenium: Severe deficiencies of selenium definitely cause muscle disease, but the jury is still out on how less-dramatic deficiencies might influence muscle function and performance. One thing is for sure. Both of these key antioxidants are important in protecting muscle tissue from damage from the high levels of free radicals generated during exercise. Let’s put it this way: If you have a horse with tying-up problems, the last thing you need to do is add to the horse’s muscle damage by failing to provide appropriate levels of these two crucial nutrients.
B Vitamins: B vitamins are essential for the processing of fats and carbohydrates to generate energy. It’s not likely that a B deficiency ever exists to the point it would cause tying-up, but hard working horses likely have higher B vitamin requirements and supplementation is wise to ensure ready energy generation.
Potassium: Horses working less than two hours per day, even at high speed in hot weather, can likely meet their potassium electrolyte needs from diet if they are getting at least 5 lbs. of hay in the morning. Most average-quality hays can be counted on to provide about 7 grams of potassium per pound. A horse working long hours in the heat needs at least 50 grams of potassium a day, sometimes more.
If you know the horse isn’t likely to take in more than 5 lbs. of hay before the end of exercise, that’s 35 grams and you’re 15 grams short. If we take Perfect Balance Electrolyte as an example, an ounce provides 5.5 grams of potassium so you need to provide around three ounces of this product over the course of the day.
Sodium: Although most commercial feeds do have some sodium added, it’s not enough to come close to meeting needs in the heat. Horses doing light work need at least 2 oz. of salt/day (4 tablespoons).
Horses in medium work need 2 to 3 oz. This can be divided between the meals and as a free-choice supplement, although if your horse has not been taking salt well it’s best to either syringe it all in for a few days, or divide between syringing and in the feed.
The horse working prolonged periods in the heat should be given about 4 oz./day of salt, which translates into 45 grams of sodium. In the 3 oz. of electrolytes he’s getting (above) to help cover potassium, there is 6.6 grams/ounce of sodium so a total of 2 0 grams (rounding from 19.8), leaving you short 25 grams of sodium. Salt (sodium chloride) is 40% sodium, so you still need 2.2 ounces of plain salt on top of the electrolyte product. Do you see how easy it is to get into trouble with electrolytes if you count on a supplement to get the job done' That’s not what they’re meant to do.
Calcium and Magnesium: The working horse should get adequate, but not excessive, calcium to match his weight, age, work and growth requirements. Alfalfa, for example, can cause problems because of its natural high calcium. If you have sporadic tying-up problems, this is an area you want to have investigated. Some horses also do better with higher-than-average intakes of magnesium.
Controlling tying-up is mainly a case of paying attention to management, fitness and diet.
Rule #1. Never work the horse beyond the level of activity you know he can handle without becoming fatigued. Condition your horse for your level of activity and your competition level carefully. Most horses enjoy working and can easily be encouraged to overdo it. A horse that has pent-up energy from being confined, or one that is in training and just reaching the point where they are starting to feel fit and on their toes, may fool you with their level of eagerness.
Rule #2. Regular daily exercise is important in horses prone to tying-up. "Monday morning disease" is one of the older names for tying-up, because it commonly struck work horses on Monday morning, after having been stalled and doing no work the day before. Daily exercise is also an effective way to control PSSM. It has been found that PSSM horses exercised daily for a month had almost normal post-exercise muscle enzymes even without fat supplementation. PSSM horses kept on 24/7 turnout also had muscle enzymes return to normal without feeding any fat.
Very fit horses are also more prone to tying-up if they miss their regular work outs. In addition, horses that are in training for speed work often go through a similar high risk period when they reach the point where they are beginning to perform work at speeds that demand high anaerobic generation of energy. The reason for this isn’t entirely clear, but the solution is the same: Don’t skip work days.
Rule #3. If a fit horse is not going to get his regular exercise, drastically cut or even eliminate the grain ration on that day. Interestingly enough, horses that are stall confined for one or two days are at risk of tying-up, but if three days or longer it’s much less of a problem. This suggests there may be a factor of accumulation of a rapidly burned fuel, possibly short chain glycogen molecules. Adjusting the intake of soluble carbohydrate is another helpful strategy.
Rule #4. Pay attention to electrolyte and mineral intake to take electrolyte imbalances and dehydration out of the picture. When working for prolonged periods in the heat, don’t invite trouble by ignoring your horse’s water and electrolyte needs. A horse eating at least 10 pounds of hay before and over the course of the day’s work, with normal hay intake the day before, probably won’t need supplemental potassium. However, if it’s less than that, you may be wise to use one a good electrolyte rather than plain salt.
Deficiencies and imbalances in calcium and magnesium can also contribute to muscular irritability and cramping. Excessive high calcium is as bad as too low and may be worse since it interferes with the body’s ability to rapidly mobilize calcium from bone when needed during exercise. Horses vary widely in their sensitivity to magnesium intakes, but when magnesium is too low you can see muscular fasiculations, elevated muscle tone and elevations in muscle enzyme.
Rule #5. If the horse has recurrent episodes, get a diagnosis so you know how to proceed. When a horse has repeated episodes of tying-up and external factors have been eliminated as possible causes, you really need to know what you’re dealing with. Muscle biopsy will confirm a diagnosis of RER vs. PSSM.
For horses prone to tying-up, a reduced carb diet is wise. We suggest considering Alam, Re-Leve or Low Starch, depending upon what is available in your area.
All hard-working horses require 1 to 2 oz. of plain salt daily, plus an electrolyte balanced to sweat losses. Our favorites are Perfect Balance and ExerLyte. For added control with horses prone to tying up, we would reach first for Tie Free 24 , which covers the major nutritional bases.