Study shows airway disease more common in racehorses than originally thought

May 03, 2018

Horses are powerful runners; on average, a galloping horse easily reaches 25 to 30 miles per hour. (The fastest recorded horse speed? Nearly 44 miles per hour, by a horse named Winning Brew in 2008.)

To achieve such high speeds, horses don’t need much beyond their own powerful muscles and plenty of air. Unfortunately, new research shows that a common airway disease that limits racehorses' ability to win is even more common than originally thought.

“We looked microscopically at the lung tissue of horses that died during or just after races, and quantified the inflammatory cells within their airways,” said Luis Arroyo, a researcher at the University of Guelph. “We expected to find that the majority of the animals would have normal airways, with only a small number actually affected with the disease, but that was not the case.”

The research team found that in fact, the majority of the 95 horses they examined had inflammatory airway disease (IAD), whereas, in the past, researched suggested that just half of all racehorses were affected. Not all cases were severe, as many horses had only mild airway changes. IAD is a treatable condition, and wasn’t necessarily responsible for the horses’ deaths.

“The findings suggest that IAD does not result from unique exposure of an affected horse to the stimulus that causes the disease,” said pathobiology expert Jeff Caswell, another researcher on the study. “But rather the research suggests that all racehorses may be exposed, with inflammation of the airways experienced by many.”

The group of horses examined included thoroughbreds, standardbreds and quarter horses. All had been actively racing or training before their deaths. The study is the first to examine horses not specifically targeted for poor race performance. In fact, the horses examined had shown no troubling signs at all.

“None of the deceased horses showed obvious signs of airway inflammation in their final three races,” said Arroyo. “The research shows that inflammation is always prevalent in racehorses, even those that may or may not have respiratory signs.”

What is IAD?

IAD is the inflammation of the respiratory system during exercise. Horses don’t show any outward symptoms when they’re at rest, but after running they may cough a lot due to excess mucus in their airway. Coughing could last for a month or longer, and over time an affected horse will start to show more breathing difficulties while exercising, and take longer to recover to normal breathing rates afterwards. Most horse caretakers notice IAD when horses begin performing poorly in races.

The stimuli that triggers the disease aren’t fully understood, but are thought to be pulmonary stress, deep inhalation of dust, air pollution and persistent respiratory viral infections. Not much is known about how IAD changes the lungs of an affected horse. The researchers hope their study will help reveal some answers about how the disease develops.

“This project gives important information regarding the health status of the performing horse,” said Arroyo. “Developing a better understanding of IAD could lead to better health in horses and a more competitive horse racing industry.”