Poor Performance in The Sport Horse

Within the animal kingdom, horses are considered to be elite athletes because of their unique physiology. Since they perform at such a phenomenally high level, even the smallest change in their health can knock down their performance. These minute, often subtle effects on their health that effect performance are really challenging to detect, sometimes requiring special diagnostic tests. It is important to investigate a decline in performance right away, since it will only get worse with further athletic activities.

Common causes of poor performance are usually categorized by the body system they effect:

Clear visible symptoms that can be pinpointed to a specific body system are frequently not evident during the early stages of diseases that effect performance. Diagnosis during the early stages rests on taking a careful and precise history, detailed physical examination, and a "high-tech" evaluation of suspicious body systems.

What to Watch For

The symptoms that clue you into poor performance depend on the horse's discipline. For example:


Veterinary care should include diagnostic tests so that the specific cause(s) of poor performance can be identified and treated successfully. Because there are so many possible causes of poor performance, it is important to be logical and methodical in choosing the following examinations or diagnostic tests.

A complete physical examination and history is crucial. This may include watching the horse performing his accustomed sport, so that the veterinarian can appreciate what the owner has noted. Other tests may include:

The results of these tests will determine which of many other, more extensive diagnostic tests should be done.


Treatment of poor performance is completely dependent upon the underlying cause. Much time and money can often be saved by pursuing the cause of poor performance aggressively and early. The problems generally worsen, so watching and waiting is not a good policy. Early detection is important.

Trial or empirical treatments given without diagnostic support, often fail and costs more money in the long run.

Home Care

Home care is dependent upon the cause of poor performance.

Disease associated with the navicular bone, which resides within the hoof capsule, has shortened the athletic career of many horses. Researchers are still working hard at determining the ultimate cause of navicular disease. The accepted causes include increased pressure within the navicular bone itself and arthritis involving the navicular bone and surrounding structures such as tendons and the coffin joint surfaces. Although navicular disease has long been associated with quarter horses that possess large bodies and small feet, it is seen in most large sport horses, including racehorses and warmbloods.

Because many horses have navicular disease in both front feet, many owners do not realize that their horse is lame. Rather, they may report that the horse has developed a very short, choppy gait, a "shoulder lameness," or seems reluctant to go forward. These horses are really sore when turned on hard surfaces and actually start to limp.

In addition to being great athletes, horses are greatly allergic. Who doesn't know a horse with hives or with heaves? An early form of respiratory disease causing poor performance stems from an allergic condition as well. In certain horses that are predisposed, allergens set up inflammation in the small airways (hence the name, inflammatory airway disease, IAD). Some of the allergens we think are particularly instrumental in causing IAD include fungal spores, bacteria and their toxins, and air pollutants. The fungal spores can come from the cleanest looking hay, so proving to someone that hay was the source is a hard sell. This inflammation smolders for a long time and is generally invisible to the even the keenest observer, until the horse slows down or can't work as hard. At this time, further diagnostic tests are pursued that reveal the problem.

In horses with IAD, there are more profound changes than just inflammation. Inflamed airways transform, becoming hyperreactive, or twitchy. Essentially, they constrict more readily and to a greater degree than do the airways in normal horses. The symptoms of constriction (bronchoconstriction) are coughing and exercise intolerance.

Because horses with allergies (IAD) have endured bouts of inflammation and constriction over and over again, their airways are also thicker due to development of excessive tissue and inflammatory secretions, and thus have a narrower lumen (passageway). The narrower airways cause a bottleneck in airflow, especially during hard work, which in turn decreases the available oxygen that is needed for work.

Because horses have an enormous respiratory reserve (the amount of excess lung not called upon during rest), the effects of IAD are often not noted until the horse is asked to exercise strenuously, breath deeply, or work at higher temperatures. This is why IAD was first recognized in racehorses. However, by the time IAD takes hold and causes the horse to slow down or a long-term cough to develop, the damage done to the lungs, while reversible, may be profound. It is absolutely imperative that IAD is recognized as early as possible, or the condition could go on to cause heaves.

EIPH is very common in racing thoroughbreds and standardbreds (80-90 percent of all horses in this category). However, very few horses bleed visibly (less than 5 percent).

The causes of EIPH are widely debated. One of the most accepted theories is that the pressure in the vessels of the lungs becomes so great in racing horses, that capillaries (very small blood vessels) in the lungs actually rupture.

Another theory is that horses have a low-grade blockage somewhere in their respiratory tract (nose, throat, lungs) and they need to pull air in harder. This creates a huge vacuum in the lungs with furthers explodes vessels.

Still another theory contends that a "shock wave" travels up from the weight-bearing forefeet through the chest wall to the lungs, which shake so violently that there is rupture of vessels. Of all these theories, only the first theory has a lot of support form research studies, and from the fact that lasix, which decreases vessel pressure, seems to reduce bleeding in some studies. But he debate about the cause of EIPH and the effects of lasix go on.

Although EIPH has caused great concern to many trainers, owners and spectators, and poor performance is often ascribed to EIPH, it likely does not cause poor performance except in the few horses that bleed extensively on race day. How extensive the bleeding must be to affect performance is unknown.

EPM is caused by a protozoal parasite that invades the neural tissues of the horse. The spinal cord is most frequently affected, but the brain may also be involved.

The parasite, Sarcocystis neurona, is thought to be passed to horses when they accidentally ingest the feces of opossums. Horses do not pass on the infection to other horses or the environment. That's because S. neurona cannot complete its life cycle in the horse, thus the horse is an accidental (incomplete), "dead end" host, in technical terms.

EPM causes a wide array of neurologic symptoms. The most commonly seen abnormalities include ataxia (lack of coordination) and muscle atrophy, especially of specific muscles in the head and tongue, as well as the gluteal and quadriceps muscles.

EPM often initially appears to be a lameness that can't be localized, which is when it becomes a cause of poor performance. With time, the disease worsens, and it is recognized as a major neurological dysfunction. Most cases of EPM are bad enough that they don't allow competition, so the symptoms are picked up at rest, but some are much more subtle. In these latter cases, it can be difficult to implicate EPM as the cause, since there is much lameness related to the muscles and bones that are more likely, and yet equally frustrating to pinpoint. Keep an open mind.

Many of us know what gastric ulcers feel like. Gastric ulceration is the pitting or deep erosion of the stomach lining. It's painful, and some horses don't perform well when they have ulcers.

In nature, horses were meant to eat relatively poor quality roughage continually. Under domestication, horses are generally fed large amounts of high quality concentrates at infrequent intervals. For a horse, even 4 feedings a day constitutes infrequent intervals, unless he always has hay in front of him.

Because horses are by nature continual eaters, they also secrete gastric acid continually. When they stop eating, the acidity in their stomachs rises dramatically. It is important to note that horses that are turned out to pasture and have continual access to roughage, do not develop gastric ulceration.

Although the discovery of the bacterium, Helicobacter pylori, has been a great advance in the understanding and treatment of gastric ulceration in humans, no evidence of this bacterium has been found in horses.

Horses with gastric ulceration may show varying signs, such as poor appetite, chronic colic, poor performance, 'crabby attitude', and teeth grinding.

Respiratory Disorders

Musculoskeletal Disorders

For Neurological Disorders

Cardiovascular Disorders

Gastrointestinal Disorders

Gastroscopy (endoscopic examination of the stomach) reveals areas of reddening and erosion in the otherwise smooth, glistening surface of the stomach.

There are many potential treatments for all of the causes of poor performance. Some of the most common include:


Follow-up care depends on what your veterinarian diagnoses as the cause of poor performance. Regardless of the cause of poor performance, it is important to schedule re-evaluations as recommended by your veterinarian. A good example is to remeasure muscle enzymes in horses that have previously tied up.

It is also important to follow treatment recommendations. Do not expect overnight success. Often, specific treatments may take weeks to months to see real improvement. For example, treatment of IAD can take several weeks to months before the horse has returned to full form, and in many cases, the recognition and proper treatment can result in new lifetime marks and top performances in these horses.