Swimming: Study Found No Bleeding in Endurance-Trained Horses

Exercise-induced pulmonary hemorrhage (EIPH) or “bleeding” refers to the presence of blood in the trachea or nostrils after exercise. Exact causes of bleeding remain unknown, but one theory centers on changing airway pressures associated with intense exercise, resulting in capillary rupture in the lungs. Swimming is frequently used as a conditioning tool in many programs. Because “explosive” expiration is observed during this activity, researchers wondered if swimming is associated with EIPH.

To explore this question, 15 healthy, elite endurance horses already accustomed to free swimming as part of their conditioning program underwent airway endoscopy one hour after swimming. The presence or absence of blood was noted.

“None of the 15 horses included in the study had evidence of blood in their airways after free swimming, suggesting that swimming exercise may not induce EIPH,” explained Ashley Fowler, Ph.D., a nutritionist for Kentucky Equine Research. “However, none of the horses were examined for EIPH before the study started, so it is possible they were not predisposed to developing EIPH.”

As alluded to above, this finding might be surprising given the respiratory pattern of horses as they swim. Specifically, horses inspire rapidly, hold their breath, and then “explosively” expire. Because of this respiratory pattern, horses have a lower respiratory rate while swimming.

These breathing mechanics are different from those observed on land. Thus, swimming may benefit horses prone to EIPH, providing an alternate conditioning technique.

Horses most at risk of EIPH include racehorses as well as those participating in endurance, polo, barrel racing, and other high-intensity sports. EIPH poses a major welfare issue and is associated with poor performance.

According to Fowler, “Supplementing with the omega-3 fatty acids DHA and EPA, such as EO-3 or ReSolvin EQ, can help improve red blood cell flexibility and inflammation status, which may reduce the risk of bleeding.”

 ^*Vinardell, T., F. David, A.M. Galezowski, M. Ali, M. Qasim, S.L. Massie, P. McCrae, S. Filho, and R. Leguillette. 2023. Free swimming and exercise-induced pulmonary hemorrhage in endurance horses: A preliminary study. Journal of Equine Veterinary Science 120:104182.