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:
- The musculoskeletal system (bones, joints, and muscle)
- The respiratory system (nose, upper airways, trachea, lungs)
- The cardiovascular system (heart, blood vessels, blood)
- The nervous system (brain, spinal cord, nerves)
- The gastrointestinal system (stomach, intestines)
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:
- Dressage 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.
- Racehorses may suddenly quit during the race, slow down at the 3/4 pole, or have a general loss of form.
- Jumpers may start to refuse, or may take down, rails.
- Event horses may show poor recovery – such as prolonged high heart rate, respiratory rate, and temperature – from the more strenuous phases of the event, or may have trouble making times.
- Pleasure horses may stumble or show signs of irritation (tail swishing, head bobbing).
- Endurance horses, like event horses, may show poor recovery or inability to finish the ride.
- Overt signs of disease, such as lameness or difficulty in breathing may arise in any type of horse.
- Other signs may develop, such as going off feed, decreased manure production, 'crabby attitudes', or general loss of bloom.
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:
- Musculoskeletal / lameness examination
- Respiratory examination
- Cardiovascular examination
- Neurological examination
- Gastrointestinal and dental examinations
- Routine blood tests (complete blood count and serum chemistry panel)
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 is dependent upon the cause of poor performance.
- Degenerative Joint Disease
- Navicular Disease
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.
- Tying up Syndrome
- Inflammatory Airway Disease (IAD)
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.
- Left Recurrent Laryngeal Neuropathy (LRLN, Laryngeal Paralysis, Roaring)
The larynx or voicebox forms the passageway to the trachea (windpipe). For effective function, the larynx must be able to close while the animal is swallowing, and it must become very wide during maximal exercise to afford the greatest airflow.
- Exercise Induced Pulmonary Hemorrhage (EIPH)
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.
- Atrial Fibrillation
- 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) 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.
- Cervical Vertebral Myelopathy (CVM or Wobblers)
- Gastric Ulceration
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.
- Endoscopy of the upper airways reveals laryngeal paralysis and may show signs of bleeding due to EIPH or excessive mucous due to IAD. In order to determine if the laryngeal paralysis is actually impeding performance, it may be necessary to carry out endoscopy while the horse is working on a treadmill.
- Lung function testing or bronchoalveolar lavage (lung wash) is imperative in the detection and treatment of IAD. Lung function testing reveals if there is small airway blockage and how severe it is. Bronchoalveolar lavage will demonstrate the composition of inflammatory cells in horses with IAD, 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 IAD and EIPH.
- Nerve and joint blocks to narrow down the exact site of lameness
- X-rays of suspected sites of lameness to determine if there is evidence of DJD
- Ultrasound of tendons, ligaments, and joints to determine if there are any structural abnormalities involving these joints
- Nuclear scintigraphy to diagnose DJD and navicular disease when specific lesions do not show up on X-rays and to diagnose RER
- Specific blood chemistry tests to diagnose RER. In particular, creatine phosphokinase (CPK), an enzyme that leaks from damaged muscle cells, is elevated in horses with RER.
- Urinalysis to 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 to determine the extent of damage that has been caused by recurrent bouts of RER – the only way to definitively diagnose PSSM
For Neurological Disorders
- X-rays of the neck may show areas of narrowing or damage due to unstable vertebrae. Often, it is necessary to perform a contrast study, called a myelogram, in order to determine if there is any compression of the spinal cord.
- Cerebrospinal fluid (CSF) tap is the best way to diagnose EPM. Horses who are positive to testing for S. neurona are more likely to actually have the disease. Blood testing alone will only tell you if your horse has been exposed to the disease (in many areas, over 50 percent of horses have been exposed to S. neurona without developing neurologic disease). However, even the CSF test is fraught with many interpretation dilemmas.
- An ECG (electrocardiogram) shows the characteristic super 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 affecting performance.
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:
- Inflammatory airway disease(IAD) is best treated with a combination of environmental management, anti-inflammatory medication (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.
- Left recurrent laryngeal neuropathy is treated with surgery. However, unless the noise is truly bothersome (or prohibited, such as in hunters), it is important to determine if the LRLN is actually affecting performance. Your veterinarian can size up the problem to determine if surgery will be effective or not. The most commonly performed surgical procedure is called a tieback, in which the left side of the larynx is fixed in the semi-open position. In addition there are procedures that remove the vocal folds, and this is why horses after tie-back make a hoarse, ineffective, whinny sound.
- Exercise induced pulmonary hemorrhage 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 to 30 lbs of body weight immediately. Otherwise, there is no known reason to think that Lasix will improve performance, and there is only minimal evidence that Lasix affects 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.
- Equine protozoal myeloencephalopathy 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 to 8 weeks, but some horses have required treatment for 3 to 6 months. Full resolution may not be achieved.
- Cervical vertebral malformation. There is no real cure for CVM. Surgery to stabilize the vertebral column has been attempted, but full return to athletic function should not necessarily be expected in any case.
- 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®).
- Degenerative 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 (psGAGs), hyaluronic acid (HA), 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.
- Recurrent exertional rhabdomyolysis 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-inflammatory medication 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, thyoid supplements, and dantrolene. None of the above treatments is dependable in warding off RER. The most important thing you can do is to reduce carbohydrate intake and go easy on the horse.
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.