by Sandy Tasse, DVM, Rood & Riddle Equine Hospital in Saratoga
Inflammatory airway disease and recurrent airway obstruction in horses
Allergies have become increasingly more common in both horses and people in the last few decades. Recurrent airway obstruction (RAO) is similar to asthma in humans. The clinical signs of increased respiratory rate and effort (as seen by flared nostrils and a “heave line” which is caused by using the abdominal muscles to breathe), as well as coughing or wheezing sounds are caused by airway narrowing and increased amount of mucous production. Inflammatory airway disease (IAD) is a milder form of RAO where the horse will not have an increased respiratory rate at rest but may cough and have poor performance.
The exact causes of RAO and IAD are unknown but are thought to be connected to allergens in the air, such as dust or mold from hay or shavings, or pollen from pasture plants. Some of the allergies in our equine friends may even be human induced. Concerned owners trying to micro-manage a horse’s daily routine can cause more harm than good. This can unintentionally result in reduced amount of turnout time, too heavy blanketing, reduced amount of exercise, and increased amount of hay fed. There may also be more allergens present in a barn now compared to years ago (in the form of chemical insect control, treatment/painting of wood/metal, coatings on buckets/feeders).
However there is also the possibility that a horse can have pasture allergies. Pastures can also have many allergens such as natural pollen as well as fertilizer, seed, etc, or even treatment of wood fences. Almost everywhere you look, something could be an allergen for your horse! Luckily most horses have a normal functioning immune system and do not severely react to environmental contaminants.
Signs of IAD and RAO may develop so gradually that an owner may not notice until the horse becomes worse or exercise intolerant. Initially the horse may only have an occasional cough or a cough that becomes apparent when working in a dusty arena. A small amount of white or clear discharge may be present from the nostrils after the horse is done working. Most horses will remain normal otherwise, in terms of body temperature, eating, and drinking. Once a horse develops severe RAO where labored breathing is evident even at rest, then the horse may exhibit a decreased appetite and some weight loss (primarily due to discomfort and with the effort to keep breathing, there is almost no time for the horse to take bites of food in-between breaths). IAD can lead to RAO, but not always. Some horses will just continue with mild respiratory signs or exercise intolerance and others will develop worsening signs as the years go by.
Your veterinarian will need to make a diagnosis of IAD or RAO by performing a complete physical exam in order to record the horse’s respiratory rate and effort and listen if there are any abnormal sounds in the lungs. A re-breathing exam may need to be performed if the horse does not have an elevated respiratory effort and the lungs need to be evaluated (placing a large trash bag over both of the horse’s nostrils for a few minutes will make the horse take deeper breaths, similar to when a person goes to the doctor and they ask for them to take a deep breath while moving the stethoscope around on the chest or back). This may be followed by other diagnostics such as endoscopic exam of the upper airway and trachea to look for mucous, blood, signs of infection, inflammation, or a mechanical obstruction of the airway (paralysis of the arytenoids, cyst or growth in airway, etc). More advanced diagnostic testing can be required such as collecting a sample of fluid through the scope (BAL- bronchoalveolar lavage) or a trans-tracheal wash or performing an ultrasound of the chest/lungs. Bloodwork may also be taken to check the horse’s white blood cell count in order to rule out infection. A secondary bacterial infection can develop in horses with RAO/IAD and may need to be treated with antibiotics. There are plenty of other respiratory diseases (bacterial and viral) that can cause signs similar to RAO/IAD, which is why it is important to have your veterinarian examine your horse to make sure it is not a primary pneumonia or upper airway infection.
Once a diagnosis of RAO or IAD is made, treatment can be initiated. Usually the exact cause of the RAO/IAD cannot be pinpointed and instead management of the horse’s environment and medications to lessen the clinical signs are used. This is one disease in which the owner can make a huge difference by management of dust and allergens in the barn, arena, and horse’s feed. Things in the barn that can be changed to reduce dust and improve airflow are:
1. Management of dust from hay: Wet or soak hay before it is fed. Only feed hay outside where the air circulation is better than in a stall. When feeding hay in a stall, place it in a ground feeder so that the horse does not have to eat it off the dusty bedding. Store hay somewhere other than above the barn where the horse is stabled. If the horse is still coughing and having trouble with dust in hay after the above is tried, hay that is better quality and less dusty may be needed. Hay may even need to be eliminated from the diet, and the horse can be fed pasture grass or soaked hay cubes or a complete senior feed.
2. Management of stall bedding: Sawdust tends to be the most dusty (as evidence by the fact it has “dust” in it’s name!). Switching to other types of bedding can help. Straw, depending on the quality, may be less dusty, along with wood shavings, however many horses will still react to these. Pelleted newspaper shavings or some of the newer pelleted shavings may be less dusty for the horse and still soak up adequate urine. Cleaning the aisle way should be done while the horses are outside. Using a broom instead of a blower will put less particles in the air or hosing down the aisle in warmer months will be the least dusty method of cleaning.
3. Management of the horse’s routine: The horse should spend as much time as possible outside if it is allergic to dust. If the horse has a pasture allergy, then turnout in a dry lot may be needed, or just trying a different pasture that may not have the specific allergen growing in it. If the horse is ridden in an arena, make sure the footing is adequately wet down before riding or switch to riding in a grass covered paddock instead. Some stables may even have artificial footing in arenas that produce very little dust when the horse works over it.
4. Increase ventilation in the barn: Keep windows and doors open at all times other than extreme cold. Use fans when it is hot or humid out (make sure the fans are elevated off the ground so they are not just blowing dust around). Keep clutter out of the barn to prevent areas from getting dirty/dusty.
5. Avoid micro-management of the barn. Micromanagement of in-climate weather and keeping a horse stalled more frequently leads to exposure to more dust and decreased airflow in the barn compared to outside. Energy is better spent in using methods to control dust and mold and keeping horses in an environment with clean air, rather than watching the thermometer. Unless it is precipitating out, a horse will be better off with a light blanket and turned out then kept in all day because of cold. If a horse has a turnout shed and a good winter coat, he/she will be happier getting at least some turnout time even on very cold days. A stalled horse may become restless and pace, which will create more dust in the barn.
After the environment has been adequately changed to suit the horse’s needs, then medications can be used as a supplement to control the horse’s breathing during worse episodes. Corticosteriods such as dexamethasone and prednisolone are the most commonly used. They will help decrease airway inflammation, irritation, and mucous production. Other medications to help the horse breathe easier would be bronchodilators such as clenbuterol and albuterol. They will help expand the airway (to counteract the narrowing that occurs with RAO) to allow the horse to take in more air with each breath.
In severe cases, Corticosteriods can be used in an inhaler, similar to how people with asthma use an inhaler. The only difference is the horse has to wear a specially made mask that covers the nostrils. When you give a few puffs of the inhaler into the mask, you then wait for the horse to passively breathe it in during their next breath. Without the mask, it would be nearly impossible to time the administration of the inhaler with the horse breathing in, and have the horse receive the majority of the medication. There are some herbal supplements that give claim to helping a horse breathe better and omega 3 fatty acids can help decrease inflammation. For horses that are unable to receive steroids (such as pregnant mares or horses with metabolic syndrome that may be prone to founder), alternatives such as pseudoephedrine (Tri-Hist Granules) and Banamine to control inflammation can be used, however they tend to be less effective.
One of the most important points to remember is that RAO and IAD tend to be chronic conditions. Once the environmental changes have been made and the horse’s breathing and performance improved, those changes have to be maintained for the rest of the horse’s life. Medications can act as an aid when the horse is at it’s worst (especially for seasonally induced allergies), but maintaining the environment is the best way to have positive results. If you do not maintain the environment, once the horse comes off medication, the clinical signs will worsen again and you will have to start over. Despite the life-long commitment, managing and controlling RAO/IAD can be done so that horses can return to their previous performance level.
