Allergies to dust, pollens, grasses, mites and many more common allergens are the bain of many people and animals, especially stabled horses, who often suffer from chronic coughs and wheezes which limit performance and ultimately quality of life for many horses.
Historically they have been classified by the type and time of the reaction, either called Seasonal Pasture Associated RAO, straight RAO, or even Congestive Obstructive Pulmonary Disease (COPD), plus or minus bacterial involvement. There is also an underlying genetic component by which certain genes make individuals more or less responsive to these allergens, creating a massively wide scope for the disease. The progression towards terming the entire disease 'Equine Asthma's should help to simplify it, and allow us to focus on the factors within our control.
1) Controlling an excessive reaction: Either due to a horse's genetic predisposition or to a massive challenge severe acute reactions may require smooth muscle relaxants just to allow enough air intake to stay alive. Once the acute phase has been avoided it's about reducing the longer term exposure and the excessive reaction with a combination of oral bronchodilators, inhaled steroids (in either 'puffer' form, or nebuliser), oral steroids (which although not without their side-effects, haven't not actually been proved to be a trigger in laminitis) and in very rare cases antibiotics.
2) Controlling the environment. While this is difficult in cases where there is a reaction to a pollen blowing in the wind, it is often much more severe in stabled horses. Therefore stable (and stable surrounds) management becomes critical.
For some good stable management advice please read the attachment from Boehringher on RAO Environmental Management