Researchers have determined that epistaxis—the most severe form of exercise-induced pulmonary hemorrhage (EIPH) in which blood runs from the horse’s nostrils—has a genetic basis. And, according to a group from Australia, a combination of genes as well as exterior influences can lead to epistaxis.

“Epistaxis is most likely influenced by multiple genes that each contribute a little bit to its occurrence,” said Brandon D. Velie, PhD candidate in equine genetics at the University of Sydney. “For epistaxis to be expressed, a horse would not only need these genes, but it would also have to be exposed to the right environmental risk factors.”

In their recent study on epistaxis, Velie and his fellow researchers investigated more than 117,000 racehorses.

“We analyzed epistaxis because of the readily accessible records pertaining to horses that had exhibited epistaxis during racing,” he explained. “We would have preferred to explore all grades of EIPH, but this would require the scoping of every horse involved in the study and was not feasible