Horse owners might dismiss mild coughing or nasal discharge in their horses, but could these two inflammatory airway disease (IAD) signs be linked to a more serious condition? Recent research results from the University of Berne's Swiss Institute of Equine Medicine indicate that, yes, these signs could be early indicators of recurrent airway obstruction (RAO, or heaves) in horses.

For this particular study, the researchers employed a scoring guide known as the "horse owner-assessed respiratory signs index" (or HOARSI) to assess clinical signs of IAD and RAO.

“The HOARSI is primarily a research instrument for epidemiological (patterns of disease) and genetic studies rather than a diagnostic tool,” reported Simone Bosshard, PhD, a postdoctoral research fellow and lead researcher of the study.

Aside from evaluating IAD signs, the researchers also set out to examine the influence of age, sex, coat color, as well as environmental factors associated with RAO development.

The team initially included three groups of horses:

  • Two half-sibling families of direct descendants of two RAO-affected Warmblood stallions; and

  • An independent population of unrelated Warmbloods (88 horses, ages 5-24).

The team later combined the half-sibling families into one study group containing 112 horses ranging in age from 6 to 15 years. Additionally, since hay feeding is a notable factor in RAO development, the researchers ensured all the horses included in their study were continually fed hay.

The horse owners in all groups were interviewed and given the HOARSI on two separate occasions (averaging just over two years apart). After the final interviews, the researchers found that while many horses did not develop RAO within the short time span, some did.

Study findings include:

  • In the half-sibling group, 35% of horses with nasal discharge and 43% of horses with nasal discharge and coughing combined developed RAO within the study period, while only 7% of horses without respiratory signs developed RAO;

  • In the independent population, 25% of horses with occasional coughing developed RAO, while only 3% of horses without any respiratory signs developed RAO; and

  • Age, sex, coat color, and bedding had no effect, and it was unclear as to whether time spent outdoors had any effect on RAO development in these horses.

The researchers concluded that “mild but persistent respiratory signs, particularly occasional coughing, can indicate an increased risk of developing RAO,” especially if the horse has a family history of RAO. They recommended having a veterinarian examine any horse with such signs persisting for more than two months.

The study, "Evaluation of Coughing and Nasal Discharge as Early indicators for an Increased Risk to Develop Equine Recurrent Airway Obstruction (RAO)," was published in the Journal of Veterinary Internal Medicine