Equine exertional rhabdomyolysis: When Muscle Soreness Warrants a Vet Visit

What is a cross-shock in horses?

Every horse person has at least once heard of cross-flexion , cross-stroke, kidney stroke or lumbago. The term " holiday sickness " has also become established in common parlance, as a horse can suffer from a cross-flap, especially during heavy workloads after days spent standing. In the past, it mainly affected working horses when they had to return to work on Monday after the weekend (hence the name Monday Morning Disease).

A cross-flexion is an inflammation of the back muscles that outwardly resembles a severe muscle ache. In the case of an acute cross -flexion, the horse has severe pain and cramps, the muscles in the back and kidney area are as hard as a board and the horse no longer wants to move.

Cross-flexion is classified as an exercise-induced myopathy, i.e. a muscle disease caused by physical activity. However, there is more to cross-flexion, as we will see below. It can also be divided into two main forms: there is the sporadically occurring cross-flap and the chronic, genetic disease, which is also known as PSSM type I and II.

Symptoms - how can I recognize a horse's cross-shock?

Whereas in the past, cross founder mainly affected working horses such as cart horses or pit ponies, today it mainly affects well-trained sport horses. If we take a look at the acute onset of cross founder, it occurs suddenly at the beginning of physical exertion after a long period of rest.

The main symptom of cross-flexion is an unwilling horse that no longer wants to move or can no longer move under its cramping muscles. It stands still like a sawhorse.

When and how intense the symptoms appear depends on the severity of the course of the disease. The symptoms differ depending on the mild, moderate and severe course of the disease:

Cross-flap with mild course:

• Symptoms occur less than 10 minutes after starting exercise
• Unrest
• Stiff, clumsy gait
• Especially hindquarters stiff and lame
• Urine is straw yellow

Cross-flap with moderate progression:

• Symptoms occur between 15 and 30 minutes after the start of exercise
• Horse stops, becomes unwilling to move
• Horse starts to sweat
• The back and kidney muscles spasm
• Some horses buckle with their hindquarters
• The urine is orange to light brown

Cross-flap with severe course:

• Symptoms occur between 30 and 60 minutes after the start of exercise
• The horse is unable to move
• The horse pushes its back away and spreads its legs out forwards and backwards like a sawhorse.
• The hindquarters only move in an uncontrolled manner
• If the horse is lying down, it's stuck
• Heavy sweating, fever and palpitations
• The severe loss of fluids leads to muscle cramps with colic-like behavior
• The back muscles are as hard as a board
• Urine is brown to even black

In the worst case, the horse is stuck and can no longer stand up due to the muscle spasms. If left untreated, the horse can succumb to death. It can also die of organ failure due to a blocked kidney.

Causes of a cross-flap - How does a cross-flap develop?

Cross-flexion in horses is one of the stress myopathies, but unlike ty-up syndrome, its cause is rooted in the metabolism. It is therefore more of a metabolic disorder: if the horse is fed too many carbohydrates, which cannot be broken down into glycogen and utilized by the horse, these accumulate excessively in the muscles. Too much glycogen in the muscles prevents oxygen transport and thus the removal of waste products and toxins. This acidic environment increases the amount of lactate in the muscle cells. This causes severe muscle soreness, which can lead to the muscle cells bursting.

The damaged muscle cells release myoglobin (muscle pigment), which passes into the blood and urine and ultimately discolors the urine. The more muscle cells die, i.e. the more severe the course of the disease, the darker the urine.

What causes the horse to have too much glycogen in its muscle cells? If the amount of feed is not reduced on days when the horse is standing, for example at the weekend, the energy is not needed. It therefore does more harm than good. The cause of an acute cross stall is therefore a lack of exercise, posture and feed management.

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The difference between cross-shock and other equine myopathies

Acute, sporadic cross stall (SER) is caused by an extreme imbalance between feeding and exercise and occurs mainly in horses with good musculature.

There is also recurrent exercise-induced cross-fatigue (RER) and genetic carbohydrate storage disease / polysaccharide storage myopathy (PSSM):

If there is an increase in the incidence of cross-flaps, it may be a stress-induced cross-flap (RER). This occurs more frequently in mares and thoroughbreds, especially racehorses. Due to excessive stress (e.g. strong external stimuli or horse races), the calcium released during muscle work can no longer be transported away. This results in symptoms similar to those of sporadic cross-fibrosis. 

PSSM is a metabolic disease that mainly affects American, heavily muscled horse breeds such as the Quarter Horse. PSSM type I is genetic and can be diagnosed using a hair test. If the horse has PSSM, it stores energy in the form of multiple sugars, which are larger than the required glycogen, and it cannot process them correctly. As with cross-flexion, the horses suffer from muscle pain during exercise and are stiff, especially at the beginning of the movement. Horses with PSSM therefore require a particularly long warm-up phase until the muscles become loose.

PSSM type II (more recently MIM: muscle integrity myopathy) is not an independent disease, but rather a collective term for all stress myopathies that cannot be clearly classified.

First aid for acute cross-fatigue

Rule number 1 for cross-flexion: Do not move the horse any further! Any further movement and strain on the muscles can further aggravate the course of the disease. The horse should be led back into its stall as far as possible. If you are out on a ride and the horse no longer wants to move, it should be brought back to the stable in a trailer.

The vet must be called immediately because, depending on the severity of the illness, every minute can count. The vet can then administer anti-inflammatory, pain-relieving and antispasmodic medication.

While waiting for the vet and if the horse is not overheating, a warming sweat blanket can keep the back and croup area warm and thus relax the muscles. A massage can also relieve the pain.

‍Diagnosisand treatment by the vet

Den Kreuzverschlag kann der Tierarzt mit einem Bluttest feststellen. Hierbei schaut er auf die Menge des Enzyms Kreatinkinase. Dieses Enzym wird bei der Zerstörung der Muskeln freigesetzt bzw. aktiviert. Die Höhe des Werts gibt also Aufschluss über die Ernsthaftigkeit der Erkrankung. Der Normalwert sollte bei < 130 U/l liegen.

If the horse sweats and urinates a lot, it loses fluids containing valuable electrolytes. To prevent dehydration and to relax the muscles, the vet can give the horse an infusion of electrolytes, antispasmodic, anti-inflammatory and blood circulation-promoting medication. Occasionally, calcium may also be necessary, which is crucial for the transmission of muscle stimuli.

Depending on the severity of the cross-fibrosis, everything may be over after a few hours or the horse may have to recover over several weeks. If the illness or recovery takes a long time, a new blood test is carried out after two weeks to check the values.

The horse can then be led slowly at a walk according to the vet's precise instructions. Standing for too long is poisonous for the horse and can trigger a recurrence of the cross-flexion when training is resumed.

The healing phase can be promoted with heat, warm compresses and massages. This provides relief, promotes blood circulation and thus the removal of waste products.

Prognosis - does my horse have a good chance with a cross stall?

If cross-flexion is recognized early and treated immediately, there is a good chance that the horse will recover. However, the prognosis is worse for horses that lie down in their spasms and then lie still. In severe cases, the horse can lie down dead or die of kidney failure.

If a cross-flap occurs repeatedly, it can lead to a lasting metabolic disorder.

So react immediately on suspicion and call your vet straight away.

Preventing cruciate rash with feeding, exercise and a training plan

The best way to prevent sporadic, acute cross-flexions is through correct training:

• Avoid brutal transitions between rest and exertion
• Make sure you warm up and warm down sufficiently
• Maintain a routine, avoid stress caused by constantly changing routines or changing environments
• Avoid long pit times
• Adapt the feed to your needs
• Avoid hypothermia of the back muscles.

It is therefore advisable to draw up a training plan to prevent cross-fatigue. This helps to create a balance between rest and exertion and to keep training regular and consistent. You should also analyze your horse's current posture. Regular, daily free exercise in open stables with grazing is crucial for the horse's health.

Performance diagnostics play a central role in this. To find out how fit your horse is, watch the performance diagnostics video in our ClipMyHorse.TV Academy:

If your horse is already in an open stable, it may be a good idea to cover it in cold, wet, windy weather. This is because cramped muscles caused by hypothermia can also be a trigger for a cross rash. After training, also make sure that the sweaty horse is given a wind-repellent and quick-drying sweat rug until it is completely dry.

Harsh ration changes and overfeeding of energy, starch and sugar contribute significantly to cross stall. On standing days in particular, the amount of feed should be reduced or standing feed that contains less starch and sugar should be used. Replacing carbohydrates with fats and oils can also be helpful.

Selenium and vitamin E can also be useful as they protect the muscle from oxidative stress. However, clarify this with your vet beforehand, as both can be overdosed.

FAQs - frequently asked questions about the cross-flap

Why does the urine turn brown in cross-contamination?

Waste products and toxins are excreted via the kidneys in the urine. If cross-fibrillation occurs with moderate or severe progression, muscle cells die. The muscle pigment myoglobin is released and reaches the kidneys via the blood and is excreted. The more muscle cells die, the more myoglobin is released or excreted and the darker the color of the urine.

How long does a cross-flap last?

How quickly a case of cross-fowl injury passes or how long the break in exercise should be depends on the severity of the disease. In mild cases, the horse will be over the disease after just a few hours. In other cases, it can take up to two months for the blood values to return to their normal range.

How long should the break be after a cross injury?

Bei einem Kreuzverschlag sollte man sich auf das Wort des Tierarztes verlassen und sich daran halten. Um die Schwere des Krankheitsverlaufs festzustellen, macht der Tierarzt einen Bluttest, um den Anteil an Kreatinkinase festzustellen. Das Pferd sollte nach einem Kreuzverschlag erst wieder belastet werden, wenn sich die Blutwerte normalisiert haben. Der Grenzwert für das Enzym Kreatinkinase liegt bei < 130 U/l.

Is a cross-flap fatal for a horse?

If left untreated, a cross stall can be fatal, for example if the horse is stuck and can no longer stand up due to the stiffened muscles. Another reason for possible death can be a blocked and exhausted kidney, which triggers organ failure.

Does a horse with a cross-flap have to be euthanized?

Not every case of cross-injury is so severe that the horse has to be put down. If treated quickly, the horse usually has a good chance of survival. However, in severe cases, the vet may decide to euthanize the horse.

The best way to prevent a cross stall and thus an emergency euthanasia is through regular and consistent exercise as well as a horse diet adapted to the amount of exercise.