Once thought of as a racehorse-only muscle disease, we now know that more equines are at risk of tying up including those who mainly hack.Equine exertional rhabdomyolysis (more commonly known as tying up) is a painful muscle disease that affects horse health. You may also hear it called azoturia, setfast or Monday-morning disease.What is tying up?Tying up in horses is often characterised by repeated episodes of muscle damage and usually happens during or shortly after exercise.Affected horses become stiff and painful, often sweat profusely and might be totally unwilling to move. The worst cases become recumbent or might even die.Tying up/azoturia in horses is described commonly in racing Thoroughbreds and has been best studied in this breed. This is likely to be because the disease affects racing performance.Several high-profile horses have been affected, such as the 2018 and 2019 Grand National winner Tiger Roll, who was reported to have had an episode as he entered the home straight in the 2018 race.However, a variety of other breeds arealso diagnosed with similar if notidentical disorders that might or mightnot have a common cause.Tying up is seen in all athletic equine disciplines such as polo, dressage, eventing and endurance riding, and can even occur while out on a hack.A horse might tie up just once in their life, but some horses are prone to repeated episodes. This is a welfare issue and can become very frustrating for horse owners and their vets.Signs of tying-up in horsesTying up is often associated with exercise and tends to occur during or immediately after a horse is worked. The signs of azoturia vary in severity but can include:Muscle stiffness or spasmsMuscles can appear suddenly hard or stiff, or can also start trembling or spasming. This usually occurs in an episodeHigh heart or breathing rateSweatingHorses that are tying-up can suddenlysweat far more than the level of exercise normally causes, and all across the bodyReluctance to move or recumbencyA horse might be reluctant to walk, becoming rooted to the spot or stiff during an episode. They might also lie down, which vets refer to as being recumbent, and they might not want to (or be able to) get upHow is urine affected?In some horses that tie up, the episode issevere enough to result in urine thatappears very dark brown or red. This isnot caused by blood in the urine, butrather by a substance called myoglobinthat is usually found inside the horsesmuscles.When a horse ties up and the muscle isdamaged, the myoglobin is released intothe circulation and is removed from thebody in urine. Myoglobin at highconcentrations in urine can damage thekidneys: on rare occasions this causes kidney failure.What should I do if my horse ties up?If you suspect your horse is having anepisode of azoturia, you should consider it anemergency and contact your vet. Whilewaiting, try to keep your horse calm. Incold weather, you can keep them warmby putting a rug on.Often a vet will confirm the diagnosiswith a blood sample, and mightadminister fluids, either via a stomachtube or directly into the vein. A vet canalso give your horse painkillers, and inserious cases they might wish tohospitalise your horse for 24-hour care.In horses that seem susceptible tomultiple episodes of tying-up, your vet mightrecommend a muscle biopsy or othertests to try to get to the bottom of theunderlying cause.Is there a cure?There is currently no cure for thisdisorder, although many horses cancontinue to perform well if managedappropriately in the long term.There is some evidence in certain breeds that horses with a susceptibility to azoturia actually have improved performance (presumably when the disorder is well controlled).Aspects of long-termmanagement include diet, exercise,prophylaxis (or administration of apreventative drug) and reducing anxiety.Diet and temperamentIt is advised to maintain horses that tie up on diets that are low in solublecarbohydrate, replacing any requiredadditional calories with fat.Themechanism by which a higher fat dietbenefits horses that tie up remainsunclear, but it has been suggested thatthis could be linked to a calming effect.Research has shown that horses with amore excitable temperament are morelikely to have an episode of azoturia.This kind of diet would involvereplacing calories from high sugar/starchfeeds like oats with high fat feeds such asrice bran, or their commercial feedequivalents.Caloric intake should bereduced in horses that are doing less workbecause of the season, or because ofillness or injury, or due to ownercircumstances (such as holidays).Genetic predispositionThe causes of tying up in horses are varied and not completely understood. A one-off episode can probably sometimes be caused by triggers such as over-exertion or eating something toxic (such as sycamore seeds or seedlings).However, repeated episodes of tying up after exercise seem to be a syndrome with both genetic and environmental elements. These animals are said to have recurrent exertional rhabdomyolysis syndrome (RER)Despite this apparent genetic factor to tying up, the only currently identified genetic disorder common in the UK (at the time of writing) is type one polysaccharide storage myopathy (PSSM1), caused by a mutation in an enzyme that is involved in muscle energy metabolism.However, most horses that tie up in the UK, particularly of certain pleasure horse breeds, do not have this mutation. The gene or genes causing RER have not yet been identified.Lowering the riskIf your horse is at risk of tying up, the following preventative measures are a good idea:A regular exercise programme, with plenty of time to warm up and cool down properly.Avoid box rest if you can and ensure a careful return to work after a break.Provide plenty of turnout (but avoid lush grazing as part of the dietary management) to help keep your horse active.Reduce your horses stress levels during exercise, stabling, turnout and during transport.Be vigilant when any of these tips are not possible, for example during winter when turnout and exercise are reduced.Medication optionsStudies have shown that dantrolene, amuscle relaxant medication, given beforeexercise can help prevent episodes of azoturia insome horses that are prone to them.Depending on the circumstances, your vetmight recommend this medication.Unfortunately, despite the bestmanagement some horses will struggleto maintain any kind of athletic career,or they become a constant worry fortheir owners.Main image: copyright ShutterstockRelated contentGastric ulcers in horses: why the time of day you ride and feed is so importantHorse behaviour: 13 signs your horse is happyCan you read your horses body language?How to tell if a horse is lameThe post Tying up in horses: causes, signs and prevention tips appeared first on Your Horse.