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Equine Asthma, Heaves in Horses
Equine Asthma, Heaves in Horses
Chronic Obstructive Pulmonary Disease (COPD)
Recurrent Obstructive Airway Disease (ROAD)
Summer Pasture Associated Obstructive Pulmonary Disease (SPAOPD)
Introduction
It may start as a transient cough as the horse begins exercising. This cough usually improves later in the work regimen as the horse clears out accumulated fluid. With repeated exposure to an allergen the cough worsens and develops into a debilitating respiratory disease. A condition where the horse fights for every breath they take. Heaves is the traditional name for the difficult breathing but over the past 50 years the scientific community has put a number of differt names on it: chronic obstructive pulmonary disease (COPD), respiratory airway obstruction (RAO), and then a number of recombinations of the above. A better description of the whole process is Equine Asthma (EA) because it is an allergic pnemonitis in horses.
There is a form of EA with a different presentation probably due to a different allergen being the cause. These horses have a history of worsening when on summer pasture. This has been labeled SPAOPD (summer pasture associated obstructive pulmonary disease) and now called SPAEA (summer pasture associated equine asthma).
In all cases EA is caused by repeated exposure to inhaled allergens that begins as a cough. As chronic changes predominant the cough worsens to difficult breathing. Early recongition and management can greatly improve the prognosis of this disease. This article discusses causes, diagnosis, treatment, prognosis, and prevention of this debilitating disease.
Causes
Allergens: mold spores, pollens(?)
EA occurs throughout the world with most cases developing in response to repeated exposure to hay with high levels of mold spores in it. In some parts of the world there are reports of a form of EA that is associated with being out on summer pasture and has been called summer pasture associated obstructive pulmonary disease (SPAOPD) or now equine pasture asthma (EPA). The cause has not been identified and it may turn out to be pollens or molds associated with certain summer grasses. Found mostly in the south eastern USA it has been reported in Oregon and the United Kingdom during hot summers. Most commonly high humidity seems to potentiate EPS but there are reports of a UK form that seems exacerbated by dry hot weather.
It seems probable that molds are not the only cause of COPD, but other causes have not been proven. When critical testing is done on COPD horses almost 100% of COPD horses, respond adversely to mold spores while the controls do not. There is no doubt that other environmental factors play important but usually secondary roles in EA and may because of their effect on molds and sporulation.
Genetics
A often asked question is why some horses develop COPD and others do not while under identical management conditions. Reviews of equine family histories has found a strong genetic predisposition for developing chronic respiratory allergies. In one case a autosomal dominant form of inheritance is implicated. This has important implications for management to prevent the onset of horses predisposed and may be a considered factor in developing a breeding program.
Respiratory Viral Infections
There are two aspects of the association of virus's and EA. It has been seen where horses develop EA following a viral infection. It has been conjectured that the viral infection may have attenuated the lungs immune system making it hyper sensitive to allergens so the horse goes on to develop EA. The second aspect is Equine Herpes Virus 5 (EHV-5). EHV-5 is a chronic lower respiratory virus that causes a progressive fibrosis of the lungs. In its early stages it can resemble EA and even has a similar cytological appearance on a broncho-alveolar lavage. The biggest difference clinically in the two diseases is that EHV-5 does not respond as well to steroids and not at all to environmental management.
Clinical Signs
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