This is the nightmare of every rider: The horse suddenly walks in a stiff way, has muscle tremors and attacks of sweating. In very dangerous cases it even refuses any further kind of movement. Then the rider immediately needs to understand that the horse possibly can be affected of an Equine exertional rhabdomyolysis (also known as Tying Up or ER). If the muscles of the horse keep on moving this muscle disease can even end fatal.The symptoms of the muscle disease ER often get mixed up with the symptoms of other muscle diseases such as colic, HYPP or ataxia. The prognosis of an ER disease mostly depends on the first reaction of the rider. Only if the horse immediately stops any further movement there is a chance that the horse does not get any irreversible health problems. Therefore any rider should take some time to inform himself about this dangerous disease – so that he can protect his horse from damage and death!
Equine exertional rhabdomyolysis – what happens in the organism of the horse?
ER is triggered by a damage of the muscle metabolism. The origin is an overdose of carbohydrates. In the organism they get converted into Glucose and several units of Glucose form Glycogen. Glycogen is the energy reserve for the muscles. If the horse eats a high quantity of carbohydrates and does not move the muscles do not need the energy reserve. As a result there is a surplus of Glycogen.
The next time the horse gets moved the muscles start to work and the metabolism gets activated. The muscles use the energy of the Glycogen so that it starts to degrade. The metabolic products are lactic acids. Due to the surplus of the Glycogen also the quantity of lactic acids is much higher than it normally is. The organism cannot provide enough oxygen for the transportation of the lactic acids so that they accumulate at the muscle tissue. As a result there is an acidosis what causes a cramp of the muscles and in the end even a complete muscle failure. In case of a consistent acidosis the muscle fibers and related tissue can tear and Myoglobin (responsible for the red pigments in the blood) is set free. This protein directly enters the blood circulation until it finally gets excreted into the urine.
What are the origins for an ER?
The most often origin for an ER is an overdose of carbohydrates (grains and pellets) that leads to a surplus of the energy reserve Glycogen. Horses can be affected by an ER if they do not move for some days and just stay in the horse stable but continuously eat the same daily fodder ration. The next time the horse starts to move its muscles there is a high likelihood that this movement triggers a damage of the muscle metabolism as explained above.
Especially coach and show horses are in danger of this muscle disease. Due to their normal physical training they get a high daily ration of pellets and grains. In case of bad weather or an injury these horses stay in the horse stable without any possible movement and continue to eat the high dose of carbohydrates. Additionally voracious and overweight horses (especially between four and eight years) are often affected by an ER. They easily overeat so that they are also in danger of a colic disease. A horse owner needs to understand the symptoms and so that he can react in the correct way: If a horse suffers from colic it should to be slowly moved whereas the horse needs to avoid any kind of movement if it is affected by an ER!
Symptoms for an ER in horses
The first symptoms occur at the beginning of the training. The muscles start to move and the metabolism gets activated. The horse starts to sweat, walks in a stiff way or even refuses any kind of movement. After these symptoms the rider already needs to consider a possible ER. In the course of the disease the muscles start to tremble and the horse has a very high breathing frequency. Additionally the muscles in the area of the back and the croup are very hard and tensed. The horse has a high body temperature and due to the excreted Myoglobin the urine has a brown or even black color. In worst case the horse feels such a great pain that the tries to press down his back (he pushes his front legs to the front and the hind legs to the back). The hind legs can even break down until the horse lies on the ground. Then the horse is incapable of any movement and this can quickly end in a fatal situation.
What does the rider need to do after he noticed the first symptoms?
The rider immediately needs to descend from the horse and make sure that the horse does not move anymore. It has often been said but it is necessary to repeat it: The horse immediately needs to avoid any further movement. The first minutes after the first symptoms completely influence the course of this disease and a wrong behavior can lead to irreversible damages of the muscles. As soon as a vet is informed the horse needs to get transported to a warm place that is protected from the wind. In some cases this means that the rider even needs to organize a horse trailer for the transport. In the next step the rider can start to cover the back and the croup of the horse with blankets. The heat helps to support the blood circulation. The vet will begin with a general examination of the horse. Many horses react with panic or are frightened so that the vet often needs to administer tranquilizers. After the first diagnosis of the vet he will administer anti-inflammatory, muscle relaxant and pain-relieving medicine. Horses that sweat a lot additionally get an injection with liquids to prevent a dehydration of the organism.
After the first diagnosis of the vet a blood screen can finally determine if the horse is affected by an ER or another muscle disease with similar symptoms (colic, ataxia, laminitis, HYPP). All components of the blood and especially certain muscle enzymes (creatine kinase) get analyzed: In case of an ER the data of these enzymes are 150 times as high as normally. For comparison: After a normal training these data are only three times as high as normally! Besides the blood screen also the urine of the horse can get tested for Myoglobine.
Therapy and treatment
If the horse is affected from a light form of ER the prognosis can be quite positive. This means that the horse normally will not suffer from any irreversible muscle damages. With the help of some stabilizing medicine the horse will be able to move and walk again after only some days. It can be very helpful to make use of a “heat therapy”. All areas of the back and the croup become heated with the help of special salves or, in some stables already available, with a horse solarium. The heat supports the blood circulation and speeds up the recovery. Additionally horse owners can feed Vitamin E and Selenium. Both substances support and stabilize the muscle and the respective tissue. In any case the horse owner and the vet need to arrange a new fodder plan and the best bedding for the animal.
If the ER already caused a great damage and cramp of the muscles so that the horse breaks down to the ground the health situation of the horse is very dramatic. Horses that lie longer than two or three days on the ground without being able to stand up again only have low chances to survive this disease. In the end most of these horses die of a heart failure or a circulatory collapse. The only chance is a therapy with a special lifting mechanism that helps the horse to stand up (all 4-6 hours the weight of the horse needs to get shifted on the other side). This supports the general blood circulation so that all organs are supplied with blood.
Prevention of an ER in horses
The best and most effective prevention of an ER in horses is regular and constant workload with the respective dose of fodder. If you always feed the normal dose of grains and pellets (even if your horse only stays in the horse stable all day) you easily risk the life of your animal. Especially horses that tend to eat too much need a strict fodder plan that correlates with the daily workload. In general however you can always provide a lot of hay in the horse stable.
The winter period can be very dangerous for the horse: The times on the pasture are short and the possibility of movement for the horse is limited. When the daily workload is not long and intensive enough the horse does not have any possibility to dissipate its energy. In any case the rider carefully needs to warm up the horse before the training (especially if the horse comes out of a cold stable). This activates the blood circulation and therefore the distribution of the oxygen in the whole organism.