by Richard Knight BVetMed MRCVS
There are a number of clinical aspects that can cause poor performance in horses, which can have varying significance based on the level of athletic work. Sometimes it can be hard to diagnose a specific cause of underperformance and it is possible for more than one factor to be contributing to the problem. Equally an issue faced by a horse in a very high level of work will have a much greater effect than one in a much lower level. Annual health checks by your veterinarian at the time of vaccination can be a helpful aid in early diagnosis of certain issues that could affect future performance.
Awareness of dental disease and the impact this has on horses’ behaviour has vastly increased in recent times. Having a vet check your horse’s teeth at the time of vaccination is a relatively simple way in determining if this be the cause of any problems. Wolf teeth are small teeth that can be found just in front of the cheek teeth in some horses. Often problems are first noticed when the horse is first introduced to the bit and brought into work. They do not always cause a problem so it is not always common practice to remove every wolf tooth. However if they are causing a problem it is possible to remove them whilst the horse is sedated. Other forms of dental disease in older horses can lead to problems due to the pain it causes. For example the presence of a diastema can lead to the accumulation of feed between teeth and can be a very painful process. If neglected dental disease can lead to a large number of secondary problems, such as sinus infections, that require much more intense and lengthy treatment.
The clinical signs associated with gastric ulcers are often vague, although changes in behaviour are one of the more commonly seen side effects. The prevalence of gastric ulcers in racehorses in work has been described as 90-100% in the literature, with around 55% of those not in work being affected. Horse in lower levels of athletic work can also be affected and the risk of this can be affected by management changes. Increased levels of stress can predispose horses to this condition, whilst withholding feed can also increase the risk. This is due to the acid in the stomach being more likely to come into contact with the unprotected portion of the stomach lining. The best way of diagnosing gastric ulcers is through endoscopy. Medical treatment in combination with a few management changes can be sufficient to control the disease. Often bad behaviour associated with gastric ulcers can be reduced or resolved after a successful course of treatment. However it should be noted that the management of this condition often involves lifetime care.
Surprisingly the prevalence of cardiac problems causing limited performance is reasonably low in the general horse population. Heart murmurs can be detected on a basic physical exam and are an indication of blood being moved abnormally within the heart. They are not always a sign of disease and are often called flow murmurs. Heart murmurs can be picked up on during annual health checks and their significance to horse can be monitored over time. Further tests can be performed to investigate the effect of any heart disease and whether this could be affecting the athletic function of the horse. Symptoms of congestive heart failure arise from increased venous pressure, with jugular vein distension being one of the earlier signs to develop. Cardiac arrhythmias are another problem that need to be evaluated as they are also not always a pathological problem.
Respiratory issues are a more commonly occurring problem and can often be associated with performance limitations. The respiratory tract is divided into two main areas of concern, the upper and lower portion. The clinical presentation of disease will depend on the area affected and therefore determining this will aid in diagnosis and treatment. Partial paralysis of the larynx is a frequently seen disease when investigating poor performance. This prevents the larynx from opening fully to allow sufficient air into the trachea. Endoscopy is the gold standard diagnostic aid for this disease and exercise endoscopy is sometimes used to evaluate the extent of the problem. Nasal discharge is a commonly seen clinical sign with problems involving the respiratory tract, whilst different types will be produced based on what the underlying problem is. Coughing can also point towards a respiratory disturbance such as lower airway disease. Samples of any fluid in the lungs can be taken during endoscopy which can also provide information about what type of disease process is occurring. There are a large variety of diseases that affect both the upper and lower airways so it is important to collect all this information to aid with a diagnosis.
Lameness is one of the most frequent reasons for a vet to examine a horse and often the clinical consequences are a bit more severe than poor performance. Commonly an owner will report the horse as being stiff or reluctant to move forwards without necessarily noting lameness. Sometimes however on exam your vet will be able to notice a mild lameness that could be responsible for exercise limitations. Often mild lameness can be misinterpreted as bank pain as a change in gait will cause certain muscles in the back to undergo a change in loading and therefore lead to them becoming sore. Nerve blocks are used to try and isolate the affected area of the limb and may cause a slight lameness in one leg to become more apparent when blocking the more noticeably lame leg. Further diagnostic tools, such as radiography and ultrasound can then be used to determine the damage to specific structures. Scintigraphy and MRI can also be used to try and achieve a diagnosis if initial imagining has been unable to do so.
Other metabolic causes for a reduction in athletic performance can be infuriating to diagnoses. The clinical signs associated with them can be very vague and diagnostic tests are not always conclusive. For some blood tests can be helpful in diagnosing a problem, although it is not always that straight forward.
Overall there are a number of different reasons for poor performance in horses, some of which are harder to diagnose than others. A combination of clinical signs, physical exam and further diagnostic tests can aid in providing a reason for underperformance. It is important to try to deal with these issues as soon as possible, as early intervention often provides the quickest and best resolution.