By Kathryn Sharbrough, DVM
Heaves, inflammatory airway disease (IAD), recurrent airway obstruction (RAO), chronic obstructive pulmonary disease (COPD), and summer pasture associated recurrent airway obstruction (SPARAO) are all names you may be familiar with for horses that display clinical signs of marked lower airway inflammation and obstruction that result in coughing, increased respiratory effort at rest and exercise intolerance. Recent research has shown that these diseases demonstrate a spectrum of chronic changes to the airways in horses. Similar to asthma in people, these clinical signs vary in intensity and over time with different environments or situations.
What are some signs my horse might be displaying if they have equine asthma syndrome?
Some clinical signs seen with Equine Asthma Syndrome include: decreased performance, coughing at rest or early in exercise, increased respiratory rate, increased respiratory effort, nasal discharge, and weight loss.
Why causes equine asthma syndrome?
We don’t know the exact cause for why some horses develop equine asthma, but the development varies with the environment the horse is exposed to, feed material, season, as well as differences in individual genetics. High dust concentration from arenas, stalls, hay, feed and even pastures can contribute a variety of inorganic and organic particles that are breathed in by the horse that cause irritation and inflammation of the airways. As well, horses housed in stables are exposed to higher concentrations of aerosolized particles and gases.
How is equine asthma diagnosed?
Clinical signs that are typical of the disease can lead veterinarians to pursue further diagnostics to differentiate between diseases. Complete blood counts, thoracic ultrasound, thoracic radiographs, endoscopy, and airway cytology are used to help diagnose your horse.
What are some diseases that can cause similar clinical signs?
Other diseases that cause some of the same clinical signs include acute viral respiratory tract infections, bacterial bronchitis or bacterial bronchopneumonia, parasitic pneumonitis, exercise induced pulmonary hemorrhage (EIPH), neoplasia, and a number of upper airway diseases.
Ok, so my horse has equine asthma syndrome. How do we treat it?
Horses are treated medically in addition to implementing some management changes to help decrease exposure to dust particles and noxious gases. Some medications commonly used to treat equine asthma include corticosteroids (i.e. dexamethasone or prednisolone) in addition to bronchodilators (i.e. clenbuterol or “Ventipulmin”). These medications can also be given via an inhaler or nebulizer similar to humans. Prior to starting therapy with steroids, an active infection MUST be ruled out because of their immunosuppressive effect.
The use of bronchodilators doesn’t effectively improve airway patency but may help to reduce coughing and may help to increase the mucus accumulated in the airways. Treatment with bronchodilators should always be done in conjunction with other measures such as management changes to decrease exposure to dust and corticosteroid treatment because the underlying mechanism of the disease is related to the persistent airway inflammation.
There is some evidence to support the supplementation of the diet with polyunsaturated omega-3 fatty acids to help change the inflammatory response. Adding omega-3 fatty acids to the diet along with management changes can help decrease or resolve clinical signs.
What kind of management changes should we make?
Reducing exposure to dust will be the mainstay of management. One way to do this is to use “low dust” feed and bedding. The second way to reduce exposure will be to improve ventilation in the barn. Exposure to dry hay is one of the main contributors to airway inflammation because of all of the associated dust. By wetting the hay prior to feeding or by switching to a complete pelleted diet or haylage, you can significantly decrease your horse’s exposure to a number of unwanted dust particles. Additionally, feeding your horse on the ground instead of in a hay net will decrease your horse’s exposure to respirable dust. A study published in Equine Veterinary Journal in 2012 found that by feeding from a hay net resulted in a 4-fold increase of exposure to dust in the breathing zone compared to feeding the same hay on the ground (Ivester et al.).
A lot of these same management techniques apply to horses that have these symptoms but are out on pasture (SPARAO). Bringing these horses into a barn that has good ventilation, low dust bedding and providing low dust feed stuffs can help these horses by decreasing their exposure to the dust particles present in the pasture.
While we’ve come a long way recently in our understanding of equine asthma, we still have a lot of unanswered questions.