Equine chronic obstructive pulmonary disease (COPD) is a non-infectious respiratory disease in which inflammation in the small airways of the lung leads to impaired ventilation. COPD is possibly the most common medical condition of mature horses and is a common cause of a premature end to their athletic careers.
Normally, the lungs supply the blood with oxygen inhaled from the outside air, and dispose of waste carbon dioxide in the exhaled air, a process known as respiration. Air is breathed into and out of the lungs through the airway, which begins at the nostrils and passes down the windpipe (trachea) into the lungs. The final smallest branches of the airway, where the oxygen-carbon dioxide exchange takes place, are known as terminal bronchioles.
Most commonly, COPD occurs in cold climates where horses are kept in barns for prolonged periods of time and where hay is moldy. It is believed that COPD is caused by an allergic reaction to these molds when horses inhale them, causing an inflammation in the terminal bronchioles ("bronchiolitis").
COPD is also known by a number of other names. Each of these terms refers to some different aspect of the clinical manifestation of this important and common problem of mature horses. Other terms that are (broadly) used to refer to the same (very similar) clinical syndrome include:
A diagnosis of COPD should be considered for many problems associated with the respiratory system of mature horses. Oftentimes, observant veterinarians will detect signs of COPD in horses presented for examination for other problems. For example, during routine vaccinations, a horse may breathe with slightly increased rate and effort at rest. Clinical problems such as coughing, exercise intolerance, inappropriately increased respiratory effort following exercise, nasal discharge, and sudden-onset severe difficulty with breathing should all warrant consideration of COPD. In horses that are losing weight as a result of COPD, the weight loss is usually not as prominent as the abnormalities associated with breathing.
In many instances, the diagnosis of COPD can be made based on assessment of the horse's respiratory medical history and the results of physical examination.
Treatment for COPD is primarily aimed at controlling the enviroment and preventing worsening of signs. Some medications but be affective in reducing the signs of illness.
What to Watch For
The most common symptoms of COPD are directly related to increased resistance to air movement through the airway passages as a result of bronchiolitis. All of these clinical signs are more prominent at times when horses are exposed to antigens in the atmosphere, typically during periods of indoor accommodation.
Although there are numerous other causes of weight loss and exercise intolerance, COPD is generally the most common cause of coughing, nasal discharge, and respiratory embarrassment in adult horses. COPD is so common that, in many instances, the significance of signs of mild disease (such as intermittent coughing or slight nasal discharge) is not properly appreciated. All too often, intermittent coughing in barn-accommodated horses is attributed to an "innocuous" barn cough. In those cases, recognition and early treatment for COPD would be more effective than, as often happens, waiting until severe lung damage (irreversible lung scarring) has occurred.
Horses with COPD usually have a history of respiratory disease that has a seasonal occurrence. However, these earlier signs have typically been mild and intermittent.
Affected horses tend to manifest coughing and exercise intolerance when accommodated inside barns, bedded on straw, fed hay (especially big bale hay), or when worked in very dusty arenas. It should be remembered that the clinical manifestations of COPD are directly related to exposure to inhaled aeroantigens; therefore, a link between the time of onset of symptoms and exposure to "dust" can often be made.
Similarly, the symptoms often regress and the horse returns to normal after the provocative exposure has been removed (either deliberately or inadvertently). For horses affected with SPAOPD, the clinical expression of disease is much more likely in the summer/fall when these horses are accommodated at pasture.
Another common and misleading feature of the history of affected horses refers to the use of antibiotics. Many COPD-affected horses have been treated with antibiotics after developing symptoms of respiratory disease (cough and nasal discharge) that resemble a "cold." Although the horse may improve during treatment with antibiotics, the reason for improvement has more to do with the natural variation of symptoms of the disease than it does with the effect of the antibiotic.