Causes of Poor Performance

Causes of Poor Performance

     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.

What to watch for;

  • Horses may have trouble coming onto the bit, or may refuse to perform a maneuver that they have had no trouble with in the past.
  • Horses may suddenly quit during the event, slow down near the end, or have a general loss of performance.
  • Horse may refuse to participate.
  • Horses may show poor recovery - such as prolonged high heart rate, respiratory rate, and temperature.
  • Horses may stumble, or show signs of irritation (tail swishing, head bobbing).
  • Signs of lameness or difficulty in breathing.

Body system that is affected;

  1. The muscular skeleton system (bones, joints, and muscle)
  2. The respiratory system (nose, upper airways, trachea, lungs)
  3. The cardiovascular system (heart, blood vessels, blood)
  4. The nervous system (brain, spinal cord, nerves)
  5. The gastrointestinal system (stomach, intestines)


Muscular Skeleton System - Joint Disease

  • One of the most common causes of lameness in sport horses is joint disease, otherwise known as osteoarthritis. Areas that are often affected include the hocks, the fetlocks, the pastern joints, coffin joints, and, less frequently, the knee joints.
  • Joint disease, as the name implies, is a disease of wear and tear. The joints are lined by specialized tissue, called hyaline cartilage that is vital to smooth joint function. This cartilage can become frayed and damaged due to the mechanical wear associated with exercise. Nasty inflammation results, which furthers the damage in a vicious cycle - damage, inflammation, damage from inflammation, more damage, etc. The normally smooth glistening cartilage becomes eroded, exposing bone and causing pain. Horses show lameness that may respond to rest initially, but usually worsens with time.

Muscular Skeleton System - Navicular Disease

  • Disease associated with the navicular bone, which resides within the hoof capsule. The accepted causes included increased pressure within the navicular bone itself, and arthritis involving the navicular bone and surrounding structures such as tendons and the coffin joint surfaces.
  • 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 seem reluctant to go forward. These horses are really sore when turned on hard surfaces, and actually start to limp.

Muscular Skeleton System - Tying up Syndrome

  • It causes a painful breakdown of muscle, which is often accompanied by a high heart rate and respiratory rate, sweating, and anxiety.
  • Tying up was traditionally called 'Monday Morning Disease', because it was seen in draft horses who were given Sunday as a day of rest but fed the full grain ration anyway.
  • It is seen in horses that are intermittently rested as well as in horses that are in continual work. Theories as to the cause of Tying up include genetic defects in muscle function, carbohydrate overloading, thyroid imbalances, vitamin E and selenium deficiencies, and hormonal imbalances.
  • Horses with Tying up may show vague symptoms such as stiffness after work, a shortened stride, an odd lameness which comes and goes, stiffness and weight loss. In rare cases, this condition can cause the horses to collapse, unable to get up on their own.

Respiratory System - Inflammatory Airway Disease

  • Horses in addition to being great athletes, are greatly allergic! 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. Some of the allergens we think are particularly instrumental 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 Airways Disease, there are more profound changes than just inflammation.  Essentially, they constrict more readily and to a greater degree than do the airways in normal horses. The symptoms of constriction are coughing and exercise intolerance.
  • Because horses with allergies 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 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 effects of Airways Disease are often not noted until the horse is asked to exercise strenuously, breath deeply, or work at higher temperatures. This is why Airways Disease was first recognized in racehorses. However, by this time Airways Disease 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 Airways Disease is recognized as early as possible, or the condition could go on to cause heaves.

Respiratory System - Bleeding (EIPH)

  • Bleeding is very common in racing Thoroughbreds and Standardbreds (80-90% of all horses in this category). However, very few horses bleed visibly (less than 5%).
  • 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.
  • Although Bleeding has caused great concern to many trainers, owners, and spectators, and poor performance is often ascribed to Bleeding, it likely does not cause poor performance except in the few horses that bleed extensively on race day.

Cardiovascular System - Atrial Fibrillation

  • Horses have enormous hearts in comparison to other species, and with training, they become even larger.
  • Horse's heart also ensures that the horse has a low resting heart rate (32-44 beats per minute).
  • Both the size of the horses heart and the low heart rate contribute to the development of atrial fibrillation. In horses, atrial fibrillation is usually benign, meaning that there is no underlying cardiac disease. Occasionally, horses may develop atrial fibrillation because of problems such as leaky heart valves.
  • With atrial fibrillation, the electrical signals that ordinarily pass from the atria, the first set of filling and pumping chambers of the heart, to the ventricles, the second set of chambers, becomes disorganized. This causes the atria to beat in a very erratic fashion.
  • Because the ventricles still beat normally despite the erratic signals sent to them, the heart is able to pump adequate amount of blood at rest. But the extra little blood pumped in by the atria, while insignificant during rest, becomes important for the horse to perform strenuous exercise. For this reason, atrial fibrillation may go undetected for a very long time in horses that do light work, such as pleasure horses, trail horses, and show hunters. 

Neurologic System - Equine Protozoal Myeloencephalitis (EPM)

  • 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), 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. This is where is 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 really implicate EPM as the cause, since there are many lamenesses related to the muscles and bones that are more likely, and yet equally frustrating to pinpoint. Keep an open mind.

Gastrointestinal System - Gastric Ulceration

  • Many of us know what gastric ulcers feel like. Gastric ulceration refers to 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, H. 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.

Veterinarian may perform the following tests;

  • For respiratory disorders:
    • Endoscopy of the upper airways will reveal signs of bleeding.
    • Lung function testing or bronchoalveolar lavage ("lung wash") is imperative in the detection and treatment of Airway Disease. Lung function testing reveals if there is small airway blockages, and how bad it is. Bronchoalveolar lavage will demonstrate the composition of inflammatory cells in horses with Airway Disease, and red blood cells or their break-down products in the horse with EIPH.
    • X-rays of the chest may show areas indicating inflammation and thickened lung tissue in horses with Airway Disease and EIPH.
  • For musculoskeletal disorders:
    • Your veterinarian will flex your horse's legs to see if he can pinpoint the site of lameness
    • Nerve and joint blocks are necessary to narrow down the exact site of lameness.
    • X-rays of suspected sites of lameness will help to determine if there is evidence of DJD.
    • Ultrasound of tendons, ligaments, and joints will let your veterinarian determine if there are any structural abnormalities involving these joints.
    • Nuclear scintigraphy will help to diagnose DJD and navicular disease when specific lesions do not show up on x-rays. It can also be useful in diagnosing RER.
    • Specific blood chemistry tests can help to diagnose RER. In particular, creatine phosphokinase (CPK), an enzyme that leaks from damaged muscle cells, will be elevated in horses with RER.
    • Urinalysis will detect evidence of damaged muscle cells in horses with RER. The most common finding is a discolored, brown-red urine that contains byproducts of muscle breakdown such as myoglobin.
    • Muscle biopsy may be necessary to determine the extent of damage that has been caused by recurrent bouts of RER, and is the only way to definitively diagnose EPSM.
  • For cardiovascular disorders
    • An ECG (electrocardiogram) will show the characteristic very irregular rhythm of atrial fibrillation.
    • An echocardiogram is often recommended to determine if there is any underlying cardiac disease in horses with atrial fibrillation.
    • A treadmill stress test with an ECG and echocardiogram may be useful to determine the extent to which the cardiovascular system is contributing to poor performance.
    • A stress test can be performed in some institutions to see if a heart problem is effecting performance.
  • For gastrointestinal disorders
    • Gastroscopy (endoscopic examination of the stomach) will reveal areas of reddening and erosion in the otherwise smooth, glistening surface of the stomach.


Treatment In-depth;

  • Inflammatory Airway Disease is best treated with a combination of environmental management, anti-inflammatories (corticosteroids), and judicious use of bronchodilator drugs. This often means taking the horse off hay, and replacing hay with special hypoallergenic hay, hay or alfalfa cubes, or a complete pelleted ration. Alternatively, you can soak the hay, but it doesn't always stave off the breathing in of fungal spores by the horses. Today, the most effective method to treat the airways of horses with IAD is to give aerosols, just like the puffers used by asthmatics.
  • Bleeding EIPH is commonly treated with Lasix, which is a diuretic. Studies have shown that Lasix may improve performance due to its effect to cause the horse to urinate, and thus shed 15-30 lbs of body weight right off the start. Otherswise, there is no known reason to think that Lasix will improve performance, and there is only minimal evidence that Lasix effects the course of EIPH. Some horses appear to respond to rest, as well.
  • Atrial fibrillation is treated with a drug called quinidine. Because quinidine is actually quite a toxic substance, it is necessary for this treatment to be administered under constant veterinary supervision. Most horses with benign atrial fibrillation will respond favorably to quinidine administration.
  • EPM  must be treated with anti-protozoal drugs. The most commonly used combination is pyrimethamine (Daraprim) and sulfa drugs. Other anti-protozoal drugs are currently still in the experimental stages. Treatment for EPM ordinarily must be continued for a minimum of 6-8 weeks, but some horses have required treatment for 3-6 months. Full resolution may not be achieved.
  • Gastric ulceration should be treated with a combination of management changes (more roughage, less concentrate in the diet, more turnout), and drugs that decrease acid production in the stomach. Some of the most commonly used drugs include cimetidine (Tagamet), ranitidine (Zantac), and omeprazole (Gastrogard).
  • Joint Disease can be treated with a combination of training changes (usually, decreasing the concussive workload), anti-inflammatories such as phenylbutazone and corticosteroids (corticosteroids should be reserved for low motion joints such as the lower hock joints), and physical therapy (warm water soaks before work, cold water after, massage, range of motion exercises). Cartilage protectants, such as glycosaminoglycans, hyaluronic acid, and chondroitin sulfate can be very helpful to restore the damaged joint surface and probably provide pain relief if they are anything like humans that attest to its effects.
  • Navicular disease is initially treated with shoeing changes, which may include egg bar shoes and degree pads. Judicious use of phenylbutazone and drugs that are thought to increase blood supply to the area may also be recommended. In chronic cases that do not respond to conservative treatment, a neurectomy (cutting the nerves that supply sensation to the heel) may be recommended. Isoxpurine, a vasodilator, also seems to reduce pain in some horses.
  • Tying Up is often an emergency in the initial stages. The horse should usually be transported home, and not be asked to walk. Depending on the severity of the signs, the horse may require intravenous fluids, anti-inflammatories, and sedation. Preventative treatment of tying up is controversial. Most veterinarians will advocate steady work without prolonged stall rest, low carbohydrate diets, supplementation with minerals and vitamins, and adequate salt in the diet. Other therapies that have been promoted include vitamin E and selenium supplements to the diet, dimethylglycine (DMG), methylsulfonylmethane (MSM), acepromazine prior to work, thyroid supplements, and dantrolene. The most important thing you can do is to reduce carbohydrate intake and maintain a dependable exercise regimen for your horse.