Breathe in, breathe out. One of the main functions that keep us (and the horses we love) alive is also one of the easiest and mindless tasks we carry out on a daily basis. But for horses with airway diseases, breathing is more difficult than it seems. Recently, researchers have made strides in understanding these diseases and what helps (or does not help) control them.

"Inflammatory airway disease (IAD) is the second most common cause of loss of use in young racing Thoroughbreds," noted Laurent Couetil, DVM, PhD, Dipl. ACVIM, professor of large animal medicine and equine sports medicine director at Purdue University, during a presentation at the 2011 American College of Veterinary Internal Medicine Forum, held June 15-18 in Denver, Colo. Inflammatory airway disease affects horses of all breeds and disciplines and is performance limiting due to excess mucus accumulation in the trachea, which reduces the horse’s oxygen availability during exercise.

Couetil explained that IAD is caused by exposure to particulates and irritants in the stabling environment, adding that horses housed outside generally don’t suffer from airway inflammation. In an indoor environment inhaled irritants, allergens, and ammonia fumes from urine breakdown are known to trigger airway inflammation even in otherwise healthy horses, particularly in combination with endotoxins.

Couetil described a recent study in which researchers evaluated 20 healthy Thoroughbred horses 16-24 months of age with no prior history of racing or IAD. Within three days of arrival at a race training barn, 55% had some degree of IAD, and by Day 28, only two of the 20 remained IAD-free. The researchers determined that both respirable dust in the horses’ breathing zones and ammonia accumulation in the stalls led to inflammatory changes in their airways–likely due to a horse’s immune responses to the challenge of environmental contaminants. More so, he noted that although the research team placed a HEPA filtration unit over half the horses’ stalls, the apparatus was not effective in removing dust or ammonia from the environment