A horse’s mid-section must serve as a sturdy, central link if he is to fulfil his athletic potential and avoid injury. Rachel Murray MRCVS discusses the importance of core strength and stability

As humans, we stand with our spine near to vertical so that gravity compresses our spinal column. Unlike us, a horse’s spine is near horizontal. His weighty abdominal and chest organs are pulled down by gravity, effectively hanging from the spine, and his heavy head is held out in front on the end of a long neck.

We then ask him to be an athlete, creating power through his body to connect the hindlimbs to the forelimbs, and finally we add the weight of a rider to the equation. Supporting these body parts and coordinating these levers — while all the time maintaining balance and energy — is a complex procedure for the horse, involving a range of muscles and nerves.

We are now more aware of the importance of core muscle development in providing the strong, stable base needed for correct movement and to prevent injury.

Power and lift

During each stride a horse’s back moves in flexion and extension, from side to side and in slight rotation.

The bigger the horse’s action — whether dressage or jumping — the more the body moves and the wider this range of movement. To prevent overstraining of any areas of the body, movement must be controlled and stabilised. A stable platform is vital so that the additional weight of the rider does not cause the back to overextend during the stride.

The horse uses both large and small core muscles to maintain this stability and move athletically.

Extension of the back occurs when the large muscles on the top of the back are contracted. The large muscles underneath the spine enable flexion of the back, support the rider and help counteract the pull of the abdominal contents. These are assisted by the muscles that flex the lumbosacral joint behind the saddle, including the iliopsoas muscles.

In addition to controlling the movement of the spine, the core muscles are important for raising the thorax (chest) of the horse relative to the floor — literally lifting the withers. Because the horse does not have a collarbone, the muscles that attach his forelimbs to his trunk must contract to create lift.

The stronger he is through his core, the more easily he can transfer power from his limbs through his body to perform movements or generate lift.

Creating stability

Poor core strength can result in a number of problems.

A very flexible young horse usually starts with a wide range of motion, giving a very elastic appearance. The more extravagant the action, the more critical core muscle development becomes to stabilise movement and protect the horse from injury.

Likewise, the less balanced the rider or the heavier they sit, the greater the risk to a horse with a very mobile and unstable back. If the back is extended too far, the dorsal spinous processes can impact on each other and form kissing spines.

Although we can see evidence of large muscle development through a good topline and a tight abdomen, the small muscles lying close to the spine are less visible. These include the multifidus muscles — vital for managing subtle movement.

When a horse is working correctly, the multifidus muscles become well developed because they are in constant use. When back pain occurs, however, the multifidus muscles are used less and tend to atrophy — becoming small and scarred, rather than functional.

Control of subtle movement for stability then decreases and the larger, less effective muscles are used. These become tense and can spasm, which can be felt by palpating the horse’s back.

Getting physical

Development of core muscle strength can be assisted by correct day-to-day management.

Encouraging the horse to have his head down and his back in flexion will stretch his topline and use core muscles. Simply feeding his hay and hard feed from the floor in his stable and encouraging turnout will help.

Stable-based exercises are useful for horses in work, following the principles of core muscle development. These include a range of baited (carrot) stretches, lifts, flexions and tail pulls, and are generally safest to do when a horse is already warmed up.

Groundwork exercises are particularly effective in switching on the correct muscle patterns without the strain and complication of a rider. These could include pole work at walk, exercise on a water treadmill or with a training aid such as a Pessoa. The maximum benefit is likely to be obtained by developing these exercises under the direction of a physiotherapist with an interest in core muscle development.

Ridden exercise with the horse’s back flexed and his head down will encourage correct posture and core muscle use, as will correctly performed downward transitions and half halts, pole work and gridwork. If the rider or saddle restricts the horse from lifting his back, however, he will be unable to perform the exercise correctly and will use the wrong muscles.

Tactile stimulators can be used under the direction of a physiotherapist to “remind” a horse to use certain muscle groups during exercise. Proprioceptive tape placed on the skin over selected muscle groups, or elasticated bands around the abdomen or quarters, can assist with switching on the right muscle groups.

Functional electric stimulation, under veterinary and physiotherapy direction, has been used effectively to improve patterns of core muscle use in some horses with back pain.

Ref: Horse & Hound; 15 October 2015

Muscular disorders can take many forms, from slight stiffness and spasmodic pain to a more serious and debilitating condition now linked — unlikely as it might sound — with the seeds of sycamore trees.

Luckily, our understanding of these equine muscle diseases – known as myopathies – has evolved considerably over the past few years. Exertional rhabdomyolysis (ER), often called tying-up, was once thought to be a single disease entity. But it is now clear, from the evaluation of skeletal muscle biopsy samples, that there are several very different muscle disorders that can lead to the common clinical signs.

Typically, horses that tie-up display stiffness and pain and may be reluctant to move during or shortly after exercise. Yet some of the more subtle clinical signs, such as poor performance or mild gait abnormalities, may not point to skeletal muscle disease and might easily be overlooked.

Some horses probably tie-up because of over-exertion. As in humans, however, horses prone to tying-up often have a proven or a likely genetic basis to their disease.

To date, two inherited conditions have been identified — RER and a similar condition known as polysaccharide storage myopathy (PSSM). Sequencing of the horse’s genome was completed in 2007, a milestone in the quest to unravel the genetic origin of these muscular conditions.

With further research into cause and possible treatments now coming to fruition, it’s time to take a look at what’s new in the world of muscular disorders.

It’s in their genes (probably)

Recurrent exertional rhabdomyolysis, which typically affects part and full thoroughbreds but possibly other breeds as well, has been considered a hereditary disease due to the pattern of inheritance in certain breeding lines.

Researchers at the University of Minnesota in the USA have recently identified a region of the horse’s genome – on the 16th chromosome – highly associated with the disease. Now experts are trying to hone in and identify the gene mutation.

Other genomic regions might also be involved. If these “causative genes” can be identified, specific diagnostic tests and potentially novel therapeutic treatments can be developed for this common condition.

More is not necessarily better

The condition polysaccharide storage myopathy occurs in a wide variety of breeds and results in abnormal carbohydrate inclusions (storage of carbohydrates) within the horse’s skeletal muscle which interfere with normal muscle function and can result in varied clinical signs from poor performance to tying-up.

In 2008 a mutation in a gene known as GYS1 was identified in horses with PSSM. This has led to the classification of two types of PSSM: type one that refers to horses with the gene mutation, while type two applies to horses that also have the characteristic carbohydrate inclusions but lack the gene mutation.

As not all horses with PSSM have this specific gene mutation, it seems that there are additional and currently unidentified causes.

Recent work by our research group at the Royal Veterinary College (RVC) investigated the effect of this gene mutation on the severity of muscle pathology in type one PSSM. Because each horse possesses two copies of the gene, affected horses can inherit one or two copies of the causative gene mutation.

Our study revealed that if a horse inherits two mutant copies – one each from his sire and dam – he will develop more severe pathological changes in muscle than a horse that inherits only one.

Interestingly, the extent of the carbohydrate inclusions seen on muscle biopsy does not always correlate with routine bloodwork. This emphasises the importance of muscle biopsy and genetic testing for determining severity and making informed decisions with regards to prognosis, training and breeding.

Benefits of a biopsy

Muscle biopsy remains the mainstay of diagnosis when an associated genetic mutation has not been identified. The procedure is well-tolerated and performed under standing sedation, and can yield valuable diagnostic information.

Claire Massey and other colleagues at the RVC’s Comparative Neuromuscular Diseases laboratory reported a case with a vacuolar myopathy, a muscle condition seen in humans but not previously described in the horse.

The unusual pathology was identified in a muscle biopsy submission from an eight-year-old warmblood gelding with a history of mild, intermittent ER.

This highlights the importance of submitting clinical samples to obtain an accurate diagnosis and optimise patient management.

As more samples are evaluated our understanding of equine muscle diseases should grow, with less common or currently unrecognised conditions not being overlooked.

Where are we now?

With many different causes of muscle disease in the horse now recognised, genetic testing and muscle biopsy can be valuable tools for vets — particularly in the investigation of animals that experience repeated bouts of tying-up.

Treatments and management that are suitable for one disease might not necessarily be optimal for others, so accurate diagnosis can help in making specific recommendations.

Despite the progress made over the past few years, considerably more work is required to further elucidate disease mechanisms and devise treatments that will help more horses with these common and painful disorders in the future.

Read more about muscular problems

This article was first published in Horse & Hound magazine (24 July 2014)

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Physiotherapists, chiropractors and osteopaths are keen on stretching exercises, both for people and for horses.

In humans there is good evidence that regular sessions of such therapy are beneficial.

But what about horses? Researchers in Michigan wanted to see if the effects reported in humans might be repeated in horses.

The multifidus muscle is a segmental muscle that occurs at each joint between the vertebrae and assists in stabilising the joints.

The scientists measured the cross-sectional size of this muscle at six places along the spine, from withers to pelvis, in eight Arabs.

They then trained the horses to perform 10 different stretching and bending exercises, which were repeated five times for five days a week.

The stretches were achieved by offering a piece of carrot at various points, such as low down between the front fetlocks, at the chest, at the shoulders, at the flanks and at the hocks.

The horses were encouraged to stretch to reach the carrot and hold the position for five seconds.

They were then rewarded with the carrot. The muscles were remeasured after three months.

Two fascinating results became apparent.

First, the degree of symmetry of the muscles improved after the training. Before the exercise programme, there was more difference in muscle size comparing left to right than at the end of it.

But most significantly, the size of the muscle increased in all the horses. In most, it increased all the way down the spine.

These results show that there are definite effects of such stretches, which look to be beneficial to the horse.

This veterinary article was first published in the current issue of H&H (8 December 2011)

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A warning has been issued for owners and vets to be extra-vigilant this season as cases of an often-fatal muscular condition appear to be on the rise.

Liphook Equine Hospital in Hampshire issued an alert after diagnosing five cases of atypical myopathy in a few days at the end of October. Three of the horses died.

And they are aware of a further four deaths in the Hampshire/Sussex/Surrey area.

Atypical myopathy weakens the muscles of the skeleton and heart and can present colic-like signs. Horses may shiver, sweat or collapse. They will appear weak and have dark red-brown urine.

The condition often occurs at this time of year in horses that are at grass.

Vets are not sure of the cause but it is thought to be due to an ingested toxin – possibly from a fungus or bacteria – which is triggered by the change towards winter weather.

“We’ve seen a rise in cases from previous years,” said Victoria Copas from Liphook.

“And there are some less-recognised earlier signs to look for – lethargy, vigorous head shaking and choke-like signs. If you’re concerned, contact a vet.”

And H&H vet consultant Karen Coumbe, of Bell Equine in Kent, said she has seen two cases since the beginning of the month – one died and one recovered. H&H is also aware of cases in Berkshire and Suffolk.

“It’s always a problem at this time of year but we’ve seen more this season. The main thing is to catch it early,” Karen said.

Horses diagnosed early by blood and urine tests can be treated with intravenous fluids but it has a rapid onset.

This news story was first published in the current issue of Horse and Hound (17 November 2011)

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Even fit, well-managed horses can be prone to tying-up, but muscle problems can be successfully managed to enable them to have a competitive career:

• Feed plenty of forage as this provides essential fibre. Any supplementary feed needs to be high in fibre and low in energy and fed in small amounts only. A gradual introduction of oil is often recommended as a substitute for large quantities of concentrate as this is an excellent energy source

• Keep to a regular routine of daily exercise and avoid box-rest, if possible

• Long, slow warm-ups and gradual cool-downs after exercise are beneficial for the horse’s muscles

• Reduce work if there is evidence of any respiratory viral infections in the vicinity

• Maintain a relaxed environment: some horses, particularly mares, are more prone to muscle disease when they are uptight, so minimise stress in any way you can

• Medication can help prevent the disease in susceptible animals, but it cannot be given

if competing as most medicines are likely to contain banned substances. Ask your vet for advice

If your horse is prone to tying-up, keep an eye out for the following signs:

• The horse may be stiff and reluctant to move. Sometimes he may seize up totally and in rare cases may collapse and become recumbent

• Discoloured (red-brown) urine may be passed as a result of a muscle disorder

• Sweating, pawing the ground, raised pulse and respiratory rates may be seen. There may also be local pain or muscle palpation, particularly around the powerful rump, thigh and back muscles. Can be confused with colic

• Mild cases of tying-up may be misdiagnosed as a low-grade lameness. This may only be apparent as a reduced stride length, reluctance to canter or an abnormal hindlimb action

For the full article on tying-up, see the current issue of Horse & Hound (29 April, ’10)

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Galeforce winds followed by sunny days, knee-deep snow and torrential rain — the joys of a British winter. Stormy weather can result in cases of atypical myoglobinuria, a serious muscle disorder associated with a sudden deterioration in weather conditions.

Atypical means it is a strange disease that does not behave as expected and myoglobinuria means that there is muscle damage, the end products of which are passed out in the urine in a similar way to a horse tying up with azoturia. However, unlike azoturia, this condition occurs in unworked or minimally worked horses.

Seen sporadically in a spring or autumn associated with foul weather, the key features to remember are:

• It usually affects several horses or ponies in a group kept at grass with little or no supplementary feeding.
• Outbreaks tend to appear after a period of heavy rain, when the animals may have become cold and wet.
• There is a sudden onset of stiffness unrelated to exercise and it can rapidly progress to recumbency and death. The sick horses appear very weak and tend to collapse easily, indicating muscle weakness, but affected muscle groups are not swollen or painful.
• Affected horses do not seem to be in severe pain and are usually able to eat and drink normally, even if they do not have the strength to stand up. Their pulse, temperature and respiratory rates tend to be normal.
• A clear clue that something is wrong is that their urine is an abnormally dark red to chocolate brown colour.
• Blood tests showing the muscle enzymes to be sky high, will prove the diagnosis, confirming it is a muscle disease.
• Unfortunately, there is no miracle cure and only supportive treatment, such as putting the horse on a drip or administering painkillers, is available. In any group of cases, it seems horses are either severely affected or not at all. With present knowledge, the prognosis for affected horses is poor.

Fortunately, this condition is still rare, but it causes concern, particularly if a group of horses collapses, which makes people panic about poisoning. In fact, atypical myoglobinuria is not due to poisoning, but may be linked to a toxic fungal overgrowth that flourishes in foul weather.

If one is aware of it, steps can be taken to reduce the risks. These include protecting susceptible horses by providing shelter or bringing them in when foul weather is forecast. Alternatively, ensure that they have supplementary feed, such as plenty of hay, while out at grass. Make certain that their general health is good and that problems that may influence their general condition, such as worm infestation, are under control.

• This veterinary feature was first published in Horse & Hound (1 February, ’07)

If a horse has a big wound, you can immediately see a hole and take appropriate action. If a horse has muscle pain, it is more difficult to detect and therefore start appropriate treatment.

Humans are often all too aware when they have overexerted themselves, ending up with sore muscles. We know when we need, at the very least, a hot bath, if not some painkillers or physiotherapy. Unfortunately, a horse cannot explain aches and pains, but if it has muscle pain, this will affect its ability to work properly.

Low-grade muscle damage is a common cause of poor performance. One recent survey of 348 horses evaluated for poor performance showed that nearly 20% had underlying muscle problems.

The difficulty is that the majority of these cases were not showing any obvious signs and were only detected by blood tests after treadmill exercise. So even if your horse is not performing properly, it can be hard to prove that this is due to muscle pain.

Signs that suggest that a horse may have a muscle disorder include:

• A history of stiffness; abnormal hindlimb action or shortened forelimb action
• Muscle cramping
• Pain on palpation of affected muscles
• Muscle twitches or tremors
• Muscle swelling or tenderness: not as obvious as one would think in a horse
• Exercise intolerance
• Reduced stride length
• Weakness
• Muscle wastage

Read about azoturia >>

Read about EPSM >>

This veterinary feature was published in full in Horse & Hound (2 June, ’05)

While tying up is well known on British shores, a totally different, but also possibly inherited, muscle disorder has come to light in recent years.

The condition is known as equine polysaccharide storage myopathy (often talked of as EPSM, PSSM or even EPSSM) and is linked with abnormal energy storage in muscle tissue. It has been seen particularly in Quarter Horses in America, as well as warmbloods and draught breeds.

Affected horses are thought to have an abnormally rapid uptake of glucose from the bloodstream and to store glycogen and an abnormal polysaccharide within their skeletal muscle fibres. Consequently, such horses can experience painful muscles, but how it all goes wrong is not fully understood.

Alarmingly, EPSM cases are not detectable using the blood tests routinely undertaken by vets for muscle disease. Instead, muscle biopsies are required to make a definite diagnosis. A sample is required for analysis from specific muscles in the hindquarters.

Such biopsies can be rapidly performed using local anaesthetics in conscious horses. The horse may be a bit sore for a few days, but at least a biopsy should provide a definitive answer. When viewed under the microscope by an experienced pathologist, abnormal polysaccharide inclusions can be seen in the muscle samples from genuine EPSM cases.

This is a disease that has been well recognised in America, while the first official report of four cases in the UK was published in veterinary literature only in 2003. There have been more recent reports of this muscle disease occurring in a family of Appaloosa horses in the UK.

Correspondence in the Veterinary Record suggests that the overall prevalence of EPSM may be even higher than suspected because few vets take muscle biopsies from horses with a history of tying up.

It seems that there is a low prevalence of EPSM in pure Thoroughbreds, but many pleasure and competition horses in the UK have draught or warmblood breeding and both types are prone to EPSM. It is very much a case of “if you don’t look for it, you won’t find it”.

As there are concerns that this condition could be inherited, it is sensible to consider biopsies in horses with repeated and unexplained episodes of muscle disease, particularly if there is any chance of breeding from the horse concerned.

The good news is that many EPSM and recurrent tying up cases will respond to a change in diet. This means increased fat and reduced carbohydrate (so cutting down or avoiding grain and minimising sweet hays and lush pastures), plus careful management, including plenty of turnout and regular exercise.

To be effective, a very high-fat diet is required, so it is sensible to establish whether it is really necessary before you start pouring in the oil. Horses usually respond to the dietary changes within four months, but before radically altering a horse’s diet, it is worth consulting your vet.

This veterinary feature was published in full in Horse & Hound (2 June, ’05)

Q: My 15h eight-year-old cob mare’s back legs shiver. It happens when I am putting her feet back down after picking them out. I have the farrier to her regularly, and she isn’t shod.

Is this a progressive condition and is it hereditary? I am thinking of treating her to a few equine muscle release therapy sessions, as I think they may help.

Jo Holmes MRCVS replies:Shivering describes a difficulty in raising one hind limb at a time and balancing on three legs.

It is most common in draught breeds and tends to be progressive. In its worst form, it can make shoeing and foot balancing almost impossible.

However, shivering does not necessarily make a horse unsafe to ride – several horses I know of have continued to work, even evented, to a high level despite the condition.

Shivering is generally most noticeable as a mild muscle tremor through the hindquarters and tail during movement, when picking out the hind feet or attempting hind limb flexion tests at pre-purchase examination.

Little is known about the causes, and its heritability cannot be ruledout, although this has not yet been proven.

It could be caused by nerve or muscle damage or spinal cord disease. Toxic plants – noticeably sweet pea – have been implicated in some countries, so it could be worth checking your pasture for these.

Otherwise, monitor your mare’s clinical signs carefully. I’d be interested to hear whether the muscle release therapy produces any improvement.

Q: I have owned my 12-year-old Thoroughbred mare for six months. Seven weeks ago, she ruptured the peroneus tertius muscle in her off-hind leg while turned out in the field. The treatment prescribed was three to six months’ box rest.

Her lameness is less pronounced now so the healing process seems to be under way. However, I would like to know if there is anything I can do to make her recovery as swift as possible and to ensure the muscle is as strong as it was before the accident happened.

My vet has suggested that physiotherapy or ultrasound could assist in her recuperation.

In addition to this, is there anything else I can do to help – such as walking her in-hand daily – or is it too early to start such exercise? I currently lead her out each day so she can have some grass, but walking is kept to a minimum.

Graeme Cooke MRCVS replies: A ruptured peroneus tertius muscle is a very dramatic injury initially and many people think the horse has actually fractured its limb.

Fortunately, it is easy for an experienced vet to diagnose and X-rays are usually unnecessary. Surprisingly, for such a dramatic condition, the prognosis is usually quite favourable.

However, it is very much dependent on where on the tendon the rupture has taken place.

If the rupture is near the origin or insertion (where it joins the bone) of the tendon, then the prognosis is not good.

Most commonly the rupture is near the hock, and in this case the outlook is optimistic. Your vet may be able to give you an idea as to where the rupture is.

The most crucial part of the treatment is to rest the leg completely for a period of at least eight weeks. After that, a limited amount of controlled walking exercise should be commenced for a minimum of three months.

If instability occurs, there is a high risk that the hock joint may develop arthritis.

The aim of controlled walking exercise is to allow the ordered formation of scar tissue between the ends of the tendon that are ruptured.

Usually at the end of eight weeks your vet will have an idea as to whether the tendon has united sufficiently to give a good outlook.

Most vets would say they could certainly do this by 12 weeks post injury.Your vet has suggested that physiotherapy and ultrasound would be of help. This is very true.

However, ultrasound is particularly beneficial in the early stages and you should consider maintaining physiotherapy from now on.

The most important part of the physiotherapy is the controlled walking. Seek your vet’s advice on this, but normally the exercise regime wouldn’t start until 9-10 weeks after the injury.

Read more about leg injuries:

• Understanding tendon injuries
• Understanding fetlock damage
• All about hocks