Horses with a more severe exercise-induced pulmonary hemorrhage (EIPH) show increased amounts of certain immunoregulatory proteins, called cytokines, when they race at sea level rather than higher altitudes, researchers on a South African study concluded.

Although the reason for the increase is not known, the study may help researchers understand the molecular relationship between EIPH and the immune system, said Montague N. Saulez, BVSc MS, PhD, Dipl. ACVIM, associate professor of equine medicine at the University of Pretoria, South Africa.

EIPH can be found in horses that exercise intensely, and it can negatively impact their health, increasing time off the track, and costing owners and trainers money. More than 55% of racehorses that exercise strenuously are affected. The disorder can impair a horse's performance, causing it to become anxious, swallow repeatedly, and cough because of blood that accumulates in the trachea. "Those horses with a severe lung bleed may suffer dyspnea (labored breathing) and struggle to aerate their lung," Saulez said.

Using tracheal endoscopy to examine 97 Thoroughbreds within two hours of racing, one group at high altitude and the other at sea level, Saulez and colleagues graded each horse for EIPH based on the amount of blood in the trachea. Then they collected and analyzed blood from 10 horses in each grade level, looking at the levels of cytokine mRNAs (messenger ribonucleic acids), which are critical for helping regulate cellular growth, development, and activation of the immune system and its response to inflammation