Which horses are most at risk of RAO?

Which horses are most at risk of RAO? – A look at the risk factors

Recurrent Airway Obstruction, better known as RAO (or colloquially "heaves"), is one of the most common chronic respiratory diseases in horses. If you own a horse with RAO or know someone who does, you know how frustrating and limiting this condition can be. But are all horses equally at risk? Or are there specific candidates more likely to develop RAO? Let’s take a closer look so you can recognize the risk factors and protect your horse.

What exactly is RAO again?

Before we discuss the high-risk patients, a quick reminder: RAO is a chronic inflammation of the lower airways. It is not an infection, but rather an allergy-like reaction to inhaled irritants. Think of it as a hypersensitivity of the lungs, especially toward dust, mold spores, and other tiny particles lurking in hay, straw, or dusty environments. The lungs react with mucus production, inflammation, and bronchospasms—making it difficult to breathe.

The environment is the main suspect, but not the only one

One thing is crystal clear: the environment is the decisive factor in the development of RAO. A horse constantly exposed to high levels of dust and mold (e.g., in poorly ventilated stables with dusty hay) has a massively increased risk. Regardless of breed or age—poor management can make any horse sick. However, research and practice show that certain factors can make some horses more vulnerable than others.

Age plays a role – Typically a problem for mature horses

Classic RAO typically affects middle-aged to older horses. The disease often develops insidiously and becomes visible around the age of 7 to 10 years or later. This is because it takes time; years of exposure to irritants lead to chronic strain and sensitization of the airways. Think of it like a barrel slowly filling with water—for some, it takes longer than others, but eventually, it overflows and symptoms appear. While younger horses aren't entirely "safe" (they often develop IAD – Inflammatory Airway Disease), full-blown RAO is usually an age-related ailment resulting from years of exposure.

Genetics and Breed – Is there a predisposition?

There is strong evidence that genetic predisposition plays a role. Some horses simply seem to react more sensitively to environmental irritants. While there is no specific "RAO breed," some bloodlines appear to be affected more frequently. It is often said that Warmbloods or sport horses are more susceptible. This may be partly due to genetics, but it is also linked to their typical management: they often spend more time in stalls or working in indoor arenas where dust levels are higher. Certain draft breeds are also sometimes described as more vulnerable, possibly due to metabolic traits or chest conformation.

Crucially: Genetics might load the gun, but the environment pulls the trigger.

Prevention: You have the power!

The good news is that while you cannot change your horse’s age or genetics, you have an enormous influence on the most important factor: the environment!

• Maximum ventilation: Ensure as much fresh air as possible—fresh and cool is better than stuffy.

• Low-dust forage: Focus on high-quality hay. If necessary, steam or soak it (steaming is more effective against mold spores).

• Dust-free bedding: Use alternatives to dusty straw, such as wood shavings, flax, or specialized pellets.

• Regular movement: Provide as much turnout or paddock time as possible.

Conclusion: Knowledge is protection. By optimizing your horse's environment, you are providing the most effective defense against RAO, regardless of their breed or age.