“Tying Up”

‘Tying up’, also known as Azoturia, Monday Mornings Disease or Recurrent Exertional Rhabdomyolysis (RER) is the most common muscle disorder in horses, frequently limiting performance in sport horses of varying breeds. Tying-up is basically muscle cramps, the largest muscles in the horse (back and hindquarters) are most often affected by a combination of different (it is not fully understood) mechanisms, leading to a buildup of lack of muscle oxygenation, lactic acid and muscle cell death.

‘Tying-up’ usually affects horses in a high level of work that are rested for 1 or more days and still fed a high carbohydrate:low fat diet. It most often occurs after 20-30 mins of work during the first exercise following a period of rest. However, it may also occur as a result of increasing intensity of work or unfit horses undergoing prolonged periods of exercise. Any breed of horse can be affected. It most often occurs amongst younger horses and affects mares more than males. Some horses experience only one or two isolated cases, whilst others suffer repeat episodes which subsequently limits their athletic potential.

Stress, excessive sweating, lack of drinking before and after work or not travelling well will cause electrolyte imbalances or disturbances which predispose a horse to ‘tying-up’. As can a diet high in cereals (as these contain a high potassium:sodium ratio) or deficient in certain minerals and vitamins. Some blood lines are also prone to producing horses that regularly ‘tie-up’ so there is a suspected genetic component too.

Depending on the severity of the episode, horses will demonstrate varying clinical signs from a mild discomfort and stiff gait to a very stiff gait and refusal to move or even in severe cases recumbency due to the pain. Most horses will have firm painful muscles in the gluteal, hamstring and back area, some horses will develop muscle swelling. Tying up is very painful and horses may become distressed and anxious, they may increase their respiratory rate, sweat or even show colic like behaviour.

If you are out riding away from your horse’s stable and your horse ‘ties-up’, phone for help. The horse should be transported by lorry or trailer to limit any further muscle damage. Once the horse is in a stable, keep them warm with plenty of rugs and offer water.

Diagnosis is made based on clinical signs and a blood test measuring muscle enzymes and kidney parameters. The enzymes are released from inside muscle cells when they are damaged. Myoglobin is a product also released by damaged muscle cells. This can discolour the urine brown or orange, potentially causing kidney damage if severe enough.

Immediate treatment depends on the severity of the episode but the aim is to provide pain relief, reduce further muscle damage and protect the kidneys. If mild; encourage the horse to drink (restoring electrolyte balance) and if the horse is comfortable you can walk them around to stop them stiffening up further, but do this with caution! If the horse is very painful, reluctant to move or recumbent, do not try to move the horse! This may lead to further muscle damage. Call your vet and allow them to provide pain relief and anti-inflammatories. The vet may also give acepromazine (ACP), a drug that calms the horse down and causes the blood vessels to dilate, increasing blood supply to the muscles. If the horse is dehydrated there is a risk of kidney damage so the horse may require rehydration by oral fluids or intravenous (IV) fluids. Other drugs are available to help stabilise the muscles and protect from further damage.

Prevention is better than cure and so if you have a horse prone to tying up it is important to provide a high-fat (bran and oils), low-carbohydrate (grains) diet, ensure your horse is properly warmed up and cooled down before and after work and exercise the horse every day, as one or more days of inactivity seems to preclude ERE episodes.

Vitamin E and selenium supplements can also be of benefit, as can antioxidants and other drugs and herbal supplements which your vet can inform you about.

Some horses suffer from chronic ER, these horses require further investigations to define why they continue to ‘tie-up’, this can involve repeat blood tests, exercise tolerance tests, and muscle biopsies.

Chris Baldwin, BVetMed, MRCVS

Sacroiliac Joint

Sacroiliac pain in horses is a performance limiting condition that can be challenging to diagnose and manage. To understand why horses develop this problem we first need to understand the anatomy involved.

The pelvis is a ring of bones formed of three fused bones; Ilium, ischium and pubis. The lower part of the horses back, the sacrum, is formed of 5 fused vertebrae. The sacroiliac joint (SI) is the joint where the sacrum passes underneath the top of the pelvis (tubera sacrale). The SI joint is strengthened by the ligaments; dorsal, ventral and interosseous sacroiliac ligaments. SI pain is either in-flammation of the joint or ligaments surrounding the joint. The SI joint functions to transfer propulsion from the hindlimbs to the spine, supporting the horses back and driving the horse forward from its hindquarters when in motion.

SI pain typically affects heavier, taller horses usually between the ages of 5 and 15 years old. There is no documented association between a horse’s confirmation and developing SI problems. Warmbloods, Thoroughbreds and Thoroughbred crosses are over represented, as are horses used for show jumping and dressage, which may be due to athletic demands placed on these horses during their work.

The signs that a horse maybe suffering from SI pain are subtle and insidious in onset and progression. Typically the signs are exacerbated when the horse is ridden under-saddle and can be easier to appreciate by the rider than to be seen by an observer. There may be no overt lameness to be seen. Table 1 lists the common signs of SI pain.


Common complaints related to SI pain


* Poor performance / unwillingness to work / holding back


* Lack of impulsion or animation 


* Intermittent lameness


* Reluctance to be shod or have the leg held in a flexed position for a prolonged period of time


* Poor or stilted canter, becoming disunited, taking the wrong lead leg


* Stiff through the back, refusing jumps


* Poor lateral work


* Change in behaviour or performance when worked on the bit


Diagnosis is challenging due to the mass of muscles surrounding the SI joint. A thorough physical exam by a veterinarian is required to rule out other conditions. SI pain is a consequence of a change in the mechanics of the horse’s back and hindlimbs. Therefore conditions such as suspensory ligament desmitis or kissing spines (impinging spinous processes) can be a precursor or sequel to SI pain.

Xray and ultrasound of the SI region is limited due to the anatomy. The most sensitive form of diagnosis is a bone scan (nuclear scintigraphy). The SI joint can also be anaesthetised (blocked) and if there is pain at this site an improvement maybe seen or felt.

Treatment of SI pain requires a combination of medication, physiotherapy and a rehabilitation programme. The SI region can be injected with steroids to reduced inflammation of the joint and ligaments. This will be performed by your veterinarian when required and usually requires more than one treatment. Physiotherapy and rehabilitation are important in making sure the horse works to build up strong muscles around its hind quarters so the SI region is protected and used correctly. Each horse with a diagnosed SI condition will have a tailored rehabilitation program outlining the details of exercises and time period. In feed, anti-inflammatories or joint supplements may be beneficial in reducing in-flammation and promoting healthy joints. Other treatments such as acupuncture or magnetic rugs/boots, may be of benefit however there is little published evidence supporting this.

In summary, the SI is the connection point between the horse and its hindlimbs. The condition mainly affects larger horses undertaking dressage and Show jumping. the signs of SI pain are very subtle. Diagnosis is challenging and treatment involves a combination of medication and rehabilitation.

Chris Baldwin, BVetMed, MRCVS

Atypical Myopathy

Atypical Myopathy was first recognised back in 1984 but has largely come to prominence over the last few years with outbreaks in the UK and Europe. It occurs in individuals or groups of horses at pasture and is likely caused by ingestion of seeds known as ‘helicopters’ (and possibly to a lesser extent leaves) of the sycamore tree (Acer Pseudoplatanus) that contain a specific toxin. This toxin has been identified as hypoglycin A. The amount of toxin within seeds is variable and it is not understood why some seeds have more toxin than others nor is it understood how many seeds have to be eaten for a horse to become sick. It is likely that some horses will be more susceptible than others with younger horses appearing particularly susceptible, particularly those in poor bodily condition, on relatively poor quality pasture. As older horses are less likely to become affected it may be that they develop some tolerance to the toxin.

Incidences tend to occur in the autumn and in the spring following large autumnal outbreaks and are often following a sudden adverse change in weather conditions, such as a frost or heavy rain. 

It can cause a variety of clinical signs which can present as dullness or lethargy or as a sudden onset of muscle stiffness or weakness that can progress rapidly to recumbency. Other reported signs also include reluctance to work, choke, whinnying, head tossing or an abnormally low head carriage. It can affect the diaphragm resulting in difficult or laboured breathing and some cases may show some colic like symptoms such as paddling or stretching the limbs. Due to the breakdown of the muscle urine often appears dark red and brown. If it affects the heart muscle it can result in a fast or irregular heart beat and in the worst case some horses may present as a sudden death. The mortality rates vary from 40-100% and vary from year to year.


Diagnosis is based on clinical signs alongside an increase in serum muscle enzymes (AST/CK) and the presence of red/brown urine.


Prompt diagnosis and treatment is essential if horses are to have any chance of survival. There is no specific treatment only supportive care which involves hospitalisation, intensive intravenous fluid therapy and nursing. Fluids are required to provide cardiovascular support as horses can become very dehydrated and to support the kidneys as the product of muscle breakdown (myoglobin) can affect their function and can cause renal failure. If there is concern over the kidney function then they may also be given a diuretic to help the kidneys maintain a good urine output. This condition can be extremely painful and so a variety of powerful painkillers and anti-inflammatories may be required. When horses become recumbent then they require frequent turning to encourage them to stand and to prevent sores. If they are inappetant then they are provided with an alternative source of nutrition usually by stomach tube in order to provide their energy requirements. Supplementary vitamins and minerals have also been shown to be useful in some cases.

Prognostic factors for survival are normal mucosae, no respiratory distress signs, a standing position most of the time, no temperature, and normal abdominal transit.
Factors unfavourable to a recovery include recumbency, abundant sedation, anorexia, tachycardia (a high heart rate), tachypnoea (high respiratory rate), respiratory difficulties and severe acid-base disturbances. Euthanasia may have to be considered when horses appear to have reached the stage where they are no longer likely to respond to supportive treatment.

In horses that do recover, recovery is initially slow, but most go on to make a complete recovery and return to work with no long-term effects of the disease.


Given the high mortality rate prevention is better than cure. If sycamore seeds are present in your fields then the following is advised

- Avoid letting horses graze pasture that are contaminated with the sycamore seeds. 
- Move horses out of the field to as distant a point as is practical, or stable the horses during the risk period. 
- If you are unable to remove horses from pastures then fence off areas where the seeds and leaves have fallen and offer supplementary hay but do not leave it on the ground to get wet and feed extra concentrate.
- Rake up or hoover and remove the seeds, dead leaves and saplings where possible.
- Reducing the stocking density can help to ensure there is good grazing for every horse.
- If you are suspicious that your horse may have ingested some of these seeds then call your vet out to check the muscle enzyme levels (AST/CK) to identify subclinical and pre-clinical cases.

If you suspect that your horse is showing any signs of atypical myopathy then contact your vet IMMEDIATELY. If you have any other concerns then please do not hesitate to contact your vet practice for further advice.

Images of Sycamore trees and seeds.