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.
Normal Muscle
If you haven't paid too much attention to what your horse's muscles feel like, you might not be sure how to tell if they are harder than normal or not. Normal muscles, even on an extremely fit horse, should be pliable when relaxed and should feel much like your own thigh when you are sitting down.
The chest, triceps (above the elbow), quadriceps (above the stifle) and the semimembranosis/semitendinosis (long muscles running down the back of the "butt") are the easiest to assess when the horse is standing quietly, but you have to be careful about the hind-end muscles since many horses tend to tense up when these are palpated. The muscles of the back/topline and neck tend to have a more firm feel to them because they are always working to support the frame.
The gluteals along the top of the rump are also more difficult to palpate because they are sitting under a layer of fat that will vary according to the body condition of the horse and because the skin in this region is particularly thick. However, you should be able to easily indent the gluteals too. They will just have a different feel to them.
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.
First Aid
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.
Causes
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.
