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."
Still, the team was able to both disprove common theories that claim epistaxis has no genetic link and determine that the condition has a complex hereditary basis.
While genes are not the only factors involved in epistaxis, they are a strong influence, Velie said. In fact, their research indicates that genetics have a stronger influence on epistaxis development than they do on the development of several other common conditions found in Thoroughbreds, including osteochondrosis and superficial digital flexor tendon injury.
They also found that epistaxis risk is related to a horse’s sex, age, and birth year (although the reasons for this are not yet known). In their study epistaxis did not seem to be related to the horse's trainer or jockey, race distance, track footing or condition, number of starts, or year or month of race, Velie said.
In light of this finding it’s important for breeders to make informed decisions about their breeding stock, said Velie. While there’s no need to exclude animals exhibiting epistaxis from the gene pool completely, people should assess their risk when selecting a breeding animal that carries epistaxis-related genes.
“When we consider that the Thoroughbred (racing) population is closed (no out-crossing to other breeds), we must remain conscious of the fact that the breed may not be able to afford the loss of a large number of horses from the gene pool because this may also result in a loss of a number of good traits as well as genes for epistaxis,” Velie said.
“Long-term, a far better approach would be to instead monitor the environment for those horses that we know are at a high risk and manage our breeding decisions accordingly," he continued. "Matings can be managed to prevent the breeding of individuals that are highly susceptible. This way we maintain genetic diversity and reduce the risk of producing gene combinations that result in an elevated risk of epistaxis.”
Knowing that epistaxis is hereditary could also eventually lead to better treatments, he added: “This is a vital step towards prevention and reduction of epistaxis occurrence. The next step is to identify markers of the genes that are involved. This will give us a clearer picture of the actual physiological cause. Knowing more about the mechanisms that cause a bleeding attack may then lead to the identification of novel therapies.”
The study, "Heritability of epistaxis in the Australian Thoroughbred racehorse population," will appear in an upcoming issue of the Veterinary Journal.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.