Exercise intolerance/poor performance testing

If your horse isn’t performing to the best of its ability, there may be an underlying problem that will need to be investigated by your vet. Exercise intolerance can have a number of causes and finding out what it is can be a lengthy process, but more often than not, treatment will be available to get your horse back on top form.

Some horse owners may believe their horse is just having the odd ‘off’ day or is just ‘getting old’, but actually there may be an underlying problem that can be treated.
If you are concerned that your horse is performing poorly, it might be worth calling your vet so they can investigate why your horse isn’t performing to their expected potential.
If you ask you vet to examine your horse, you can help by providing as complete a history as possible. It is sometime impossible to be certain when signs began or other significant development occurred because often the onset is so subtle, but even narrowing it down between weeks, months and years can help. It is worth mentioning changes you are not sure are significant because it is never clear what information is useful until the final diagnosis is reached. If the information is never provided, it can’t be useful!

The most common reason for poor performance is lameness or other orthopaedic issues. The second most common reason is respiratory (lung/breathing) conditions, both of the upper and lower respiratory tracts. Cardiac (heart) causes of poor performance are the least common but do exist. Although these are the most common, and will usually be investigated first, there are other causes of poor performance that do not fit any of these categories. For example, a horse recovering from an infection may not be performing very well.
An initial poor performance evaluation is probably best undertaken by your horse’s regular vet who knows your horse’s medical history. Your vet may then refer your horse on for more specialised investigations if necessary.
Tests will include the following:

  • A lameness work-up: to identify any musculoskeletal problems. This will include flexion tests and if your horse is lame, this may involve nerve and/or joint blocks and further diagnostic imaging to pinpoint the exact area that is an issue.
  • A respiratory examination: to identify any respiratory problems. This will involve listening to your horse’s lungs with a stethoscope and if a problem is suspected this may be followed up by endoscopy of the respiratory system and sending samples to the laboratory for examination.
  • A cardiovascular examination: to identify any problems with your horse’s heart. This will involve listening to your horse’s heart with a stethoscope and if a problem is suspected this may be followed up with an electrocardiogram (ECG) and an echocardiogram (ultrasound) which will pick up any abnormalities.

Lameness is a common cause of poor performance; a horse cannot perform well if there is pain or lameness present. Orthopaedic conditions can include a problem in any of the legs, but also in the neck, back or pelvis. The neck, back and pelvis form the axial skeleton, and poor performance due to this area can be even harder to detect because there is often little or no lameness present.
Firstly, your vet will check your horse over for any obvious outward signs of a problem, for example is the horse willing to place weight on all four legs, does it stand normally, is it unwilling to lift up a particular foot or move in a certain way, and does it have any pre-existing or recent injuries. Your horse will be walked and trotted in a straight line, and as long as facilities are available, your horse will be examined on both hard and soft surfaces. The latter is especially important as your horse can be observed at the canter, which is the gait in which many horses with axial skeletal problems show abnormal findings.
Following this, your vet will perform some flexion tests; the fetlocks, knees and hocks are each flexed for 45-60 seconds and after flexion the horse is trotted off while your vet checks for uneven stride length, lack of propulsion or reluctance to land on and load a particular joint. The test is positive if lameness is seen and negative if none is seen. Lameness is usually scored out of 10, 10 being a non-weight-bearing lameness where the horse is unable to move.
If you have noticed that the signs which concern you are more evident when your horse is ridden, make sure to tell your vet so they can assess your horse under saddle.
If there is no evidence to support an orthopaedic reason for the poor performance, your vet may move on to investigate the respiratory system and the heart.
If lameness is noted your vet may want to do some additional diagnostic work, such as nerve and joint blocks, to pinpoint the area of concern. Subtle lameness and problems involving the neck, back and pelvis may require further investigation using radiographs, ultrasound, thermography or scintigraphy (a bone scan). In some complicated cases, lameness may only be observed when the horse is performing, and high-speed treadmill evaluation may be necessary.

Another cause of decreased performance is a respiratory abnormality. Respiratory problems can be found in both the upper and lower respiratory tract. Information you can provide your vet includes any exercise intolerance or any noise you have heard when your horse is exercising.
Your vet will perform an external examination to check for any signs of trauma, respiratory distress, nasal discharge, etc. A re-breathing bag may be used over the horse’s nose, which makes them breathe much deeper than normal; this allows your vet to listen for abnormalities and assess how well your horse recovers from stress. Your vet will also use a stethoscope to listen to your horse’s chest to detect abnormal noises such as wheezes and crackles which indicate respiratory disease.
If these examinations suggest anything abnormal, further investigations may follow. Endoscopy of the upper respiratory tract allows direct visualisation of many structures of the nasal passages, back of the throat and the larynx (voice box). Of these, the larynx will be the most common reason for poor performance in the upper respiratory tract by obstructing the flow of air down into the lungs.
A video endoscope can also be used during treadmill exercise to diagnose exercise-induced respiratory conditions. A fairly recently developed technology, overground endoscopy (also called exercise endoscopy) is also useful; this is the same camera used for normal endoscopy but it is fitted to your horse’s bridle during ridden exercise with the rest of the equipment secured to the saddle. This is particularly useful for those upper respiratory conditions which appear normal at rest and only occur at ridden exercise.
Passing an endoscope into the upper respiratory tract also allows collection of a fluid sample from the trachea (a tracheal wash) which can be examined in the lab for signs of infection or airway inflammation. Fluid can also be collected from deeper into the lungs using a technique called a bronchoalveolar lavage, but this technique should be done in the clinic because the samples have to be preserved carefully and processed right away.
It is possible to x-ray your horse’s chest, but this will need to be done in a hospital because of the size of the x-ray machine required.

A general clinical examination of your horse will identify the presence of ventral oedema (accumulation of fluid) or weight loss which can both indicate heart failure, but are also associated with many other diseases, therefore further examination will be necessary.
One of the most important aspects of the clinical examination is checking the horses pulse to determine the rate and quality; weak or bounding pulses can indicate a problem. Your vet will also listen to your horse’s heart with a stethoscope; an increased heart rate at rest with no other cause or pain may indicate a problem.
If necessary, diagnostic tests including electrocardiography (ECG), echocardiography (ultrasound) and blood tests are used to determine what sort of heart condition your horse had:

  • Electrocardiography is a way of interpreting the electrical activity of the heart over a period of time using electrodes attached to the surface of the skin. It is a non-invasive procedure and produces an electrocardiogram that your vet will examine to check for any irregularities in your horse’s heartbeat. Continuous 24 hour monitoring is essential to detect subtle or intermittent abnormalities; however, these conditions are rarely a cause of poor performance.
  • Echocardiography on the other hand uses ultrasound to examine the heart’s structures and function. An echocardiographic examination can identify conditions such as enlargement of heart chambers, valvular disease and cardiac fibrosis.
  • Blood tests may also be useful; haematology and serum biochemistry tests can sometimes offer further information on the underlying causes of heart disease.

There are two main reasons the heart does not function properly; valve insufficiency and valve stenosis. Murmurs mean that the blood is not flowing smoothly and can be the result of valves that leak when they should be closed (valve insufficiency), or valves that do not open fully when they should be open (valve stenosis). If the heart cannot efficiently pump blood around the body, it will be most evident when the heart is working hard, i.e. when your horse is exercising.
Heart murmurs are not always significant and don’t necessarily cause a problem. Your vet will listen to the heart to detect any murmurs and then may recommend echocardiography.
The other reason the heart may not function properly is called an arrhythmia. An arrhythmia affects the electrical system of the heart, so the heart does not beat regularly or smoothly. If the electrical signals that drive the heart beating are abnormal, the heart will not receive the pulses to pump blood efficiently through the heart. The most common arrhythmia is atrial fibrillation, and it can occur intermittently. To investigate an arrhythmia, your vet will first listen to the heart to further pinpoint it, and then will recommend and ECG which provides a printout of the electrical activity of the heart. From this, the murmur can usually be identified more specifically.

There are of course cases of poor performance that do not fall into the above categories, and disappointingly, some cases for which a diagnosis is not reached. Perhaps some of the cases are the result of aging, or behavioural changes, but a proper in depth investigation gives you the best chance for finding an explanation.