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29th January 2007

Lung Disease in Racehorses – USA Article

Anyone who has ever raced horses is aware that racehorses seem unable to successfully defend themselves against the causes of lung disease. Racehorses represent a section of the equine population that is well cared for, fit and receive regular strenuous exercise. Yet racehorses are much more likely than slower, weaker, less fit horses to develop lung infections such as pneumonia, infectious bronchitis, lung abscesses.

Dorothy Ainsworth DVM, PhD. A veterinary researcher at Cornell University is looking into the reasons why.

Ainsworth has been awarded a grant from the Harry M Zufig Memorial Fund for Equine Research to investigate the mechanisms of how higher intensity exercise weakens the immune system. In her work she has found that exercise is only one component of the stress of being a racehorse.

“Most of the things that are best for reducing stress to the respiratory system are difficult to achieve in a racing environment,” Ainsworth said. But ways do exist to decrease irritants at the racetrack and to strengthen the horse’s respiratory system, including:

•Increased turn-out time;

•Better ventilation (shed row stalls as opposed to totally enclosed barns);

•Reduced dust;

•Cleaner bedding;

•Quality hay that is low in mold spores (best fed after soaking in water if there are any concerns over quality); and

•Decreased transport stress.

While some of these items may seem difficult to implement at present, it only takes one individual who alters how racehorses are trained and campaigned and who then wins to change the management of these athletes.

Recurrent airway obstruction

Perhaps the most common lung disease seen, especially among racehorses, is recurrent airway obstruction (RAO). The condition has been previously termed chronic obstructive pulmonary disease (COPD) and is known by most horsemen as heaves.

Obstruction of airways in this condition occurs as a result of chronic inflammation and spasm of the bronchioles with accumulation of mucus and dead cells (exudate).There is mounting evidence that most cases of RAO are the result of hypersensitivity of the horse’s immune system to allergens most likely found in dust or molds associated with hay. The equine athlete’s world usually creates conditions where overexposure to these allergens is common. Lack of pasture turn-out and exposure to green grass means more stall dust and hay nets, which increase the chances of developing RAO.

Affected horses exhibit a cough; thick, mucopurulent nasal discharge; wheezing and other abnormal lung sounds; weight loss; and the eventual development of increased chest muscles used to help move air through constricted, inflamed airways. Another similar condition seen primarily in young horses (less than two years of age) has been called inflammatory airway disease. It is thought that this variation of airway spasm and mucus buildup is associated with repeated bacterial infections in these growing horses and not the allergy reaction seen with RAO.

Diagnosis and treatment

Diagnosing the type of respiratory ailment a horse may have relies on ultrasound, radiology, endoscopy (putting a thin fiber-optic scope into the horse’s nostril and through its nasal passages into the trachea and larger bronchi to visualize these areas), transtracheal wash (a small tube is placed into the windpipe and fluid is flushed into the trachea and then withdrawn for examination for cell types and bacterial content), and bronchoalveolar lavage (this technique places a tube deeply in the lung airways to collect a more representative sample of the cells involved with various conditions).

Nasal polyps or masses are generally easily diagnosed because the affected horse breathes with a wheeze or noise caused by air moving in a narrow passage. Endoscopic examination usually reveals the location and cause of the problem. Other obstructive problems in the horse’s larynx are more numerous and perhaps more serious.

Conditions such as dorsal displacement of the soft palate, epiglottic entrapment, laryngeal paralysis, and lymphoid hypertrophy of the pharynx can cause swelling through the back of the throat. Infectious or viral tracheitis can be seen, as well. Strangles, a serious infection caused by the bacterium Streptococcus equi, can lead to massive pus-filled abscesses that occasionally constrict the throat or larynx.

Treatment options are then determined based on results of the above tests and usually involve antibiotics, anti-inflammatory medications, bronchodilators, and, perhaps most importantly, environmental management to reduce stress and allergen exposure.

Ainsworth and other researchers believe that they are approaching a means of helping these horses stay competitive. “We think that allergen desensitization through immunotherapy just may be a viable and safe treatment option for [RAO] in all kinds of horses, including racehorses,” Ainsworth said.

Other aspects of ongoing research are looking at various medications that boost or improve immune system function. Recently, one such new medication, Zylexis, has become available commercially in this country. Ainsworth and other researchers in this field feel that further work with immune system medications may produce even more positive results.

Kenneth L. Marcella, D.V.M., is a practicing veterinarian in Canton, Georgia

Article from: Thoroughbred Times – www.thoroughbredtimes.com – 28 Nov 2006