Researchers Study Bleeding in Australian Racehorses

In Australia, if a horse bleeds once (defined as blood visible in both nostrils) he gets a three-month ban from racing and a two-month ban from training. If he bleeds a second time, he must be retired.

Photo: Matt Goins

Bleeding from the nostrils—technically termed epistaxis—has long been recognized as a problem affecting racehorses during or after intense exercise. The underlying cause of the condition, however, remains elusive.

Looking at the official race records of horses that experienced an episode of epistaxis, an Australian research team recently sought to identify risk factors for recurrence as well as determine an epistaxis episode's impact on a horse’s racing career.

Although it's a point of great debate, veterinarians and trainers in the United States have the option of racing horses on the anti-bleeding medication furosemide (commonly known as Salix or Lasix). However, vets and trainers in some other countries don't have that option.

“In Australia, there are no race-day medications allowed in horses,” said Peter Knight, PhD, a researcher in the biomedical science department at Sydney Medical School, who teamed up with members of the University of Sydney Veterinary Science Department for the study. “If a horse bleeds once—defined as blood visible in both nostrils—they get a three-month ban from racing, and a two-month ban from training. If they bleed twice then they get a lifetime ban and must be retired.”

Incidence of Bleeding

The researchers examined the official career records of all horses that were banned for bleeding on New South Wales racetracks over a nine-year period (from August 1999 to July 2008). The overall prevalence of epistaxis amongst the racing population was approximately 0.2%, which is consistent with the estimated prevalence of epistaxis in racehorses in Australia, Knight noted.

The study results also revealed that of the horses banned for epistaxis, 41.8% experienced an incident within their first 10 starts.

“This was surprising because it’s been suggested that epistaxis might be a wear-and-tear type problem, and that horses that have done more racing are more likely to bleed,” said Knight. “But in this study there was a very high percentage that bled early in their careers.”

It could be that wear-and-tear is not a contributing factor, or that horses do not need much wear-and-tear to become bleeders, he added, noting that no direct conclusions on these hypotheses can be drawn from this study.


Of the horses that raced following their three-month ban for an initial epistaxis episode, 20.5% incurred a lifetime ban for a second occurrence. However, with the information available to them from the racing records—including the time between the previous start and the start at which the second episode of epistaxis occurred, and the change in percentage of winning starts recorded before the first bleed compared with after—the researchers could not identify any significant risk factors that might contribute to an increased likelihood of a recurrence of bleeding.

“Unfortunately, there wasn’t anything of great value that predicted whether or not a horse was going to bleed again, so we couldn’t offer any recommendations on deciding whether or not to bring a horse back after a ban, or on ways to manage a horse if it has bled,” Knight said. Other variables not captured in the racing records might have a higher predictive value, he added.

Effect on Career

Just over half of the horses (53.8%) that incurred a ban due to epistaxis returned to racing. Older horses, the researchers found, were less likely to return to racing after the first incidence than their younger counterparts. Female racehorses were also slightly less likely to return to racing, “but not for any obvious sort of reason,” noted Knight. “If you looked at all the females that were retired and all the females that returned to racing, there was about an equal percentage that went to stud from both groups, so there was no difference in their breeding careers.”

Even amongst these variables (age and sex), the effect was quite small, said Knight, perhaps reflecting the individual nature of making a decision whether to retire a horse.

The study, “Epistaxis in racehorses: risk factors and effects of career,” was published in the Australian Veterinary Journal

About the Author

Lindsay Day, REMT

Lindsay Day is a registered equine massage therapist and freelance health and science writer. She and her horse, A.J., are based in Ontario, Canada, where Day is currently pursuing an master’s of science in population medicine at the University of Guelph.

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