RAO issue 18.qxd:Jerkins feature.qxd
16/10/10
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RAO
Recurrent Airway Obstruction in racehorses R
AO is the most recently adopted term and describes what happens to affected horses, namely that they experience intermittent episodes of blockage (obstruction) of the smaller airways deep in the lung. This obstruction is caused by the muscles around the airways constricting and closing the airways down, and also by over-secretion of mucus which blocks the airways. This is very similar to what happens to someone having an asthma attack although RAO probably shares more similarities with “farmers lung” than asthma as far as the causes. The term equine COPD became less favored about 15-20 years ago as it caused confusion with human COPD. The latter is a condition brought about by smoking, and while a fair few owners, trainers, and jockeys may enjoy a cigarette, horses don’t. What brings on an “attack” in a horse with RAO? RAO is an allergic disease in which affected horses have an overreaction to things normally present in their environment, such as pollens, molds (in particular Aspergillus species) and forage mites. Interestingly, a study from the University of Berne published in 2009 showed that the most common positive reaction (around 75% of tests) was to mite allergens rather than molds. At some stage RAO horses have been “sensitized” to one or more of these allergens, so called because they produce an allergic reaction. This allergic reaction can lead to almost immediate signs of disease which are typical of RAO, including coughing, nasal discharge, increased mucus in the airways, increased lung sounds, increased respiratory rate and effort (this is where the term “heaves” comes from, describing the heaving effort of the chest and abdomen as the horse struggles to move air into and out of the lungs and the
The old name for it is “broken wind,” we used to call it COPD (Chronic Obstructive Pulmonary Disease), we refer to it more commonly as “heaves,” and the most recent term that was adopted by vets and scientists who were studying it is Recurrent Airway Obstruction (RAO). Many of these terms are still in common use, and different groups of people involved with horses will possibly recognize the different terms for what is exactly the same condition. By Dr David Marlin
Nasal discharge is one of the typical signs of RAO
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