Chris Whitton: Deaths highlight risks in horse racing

Zac Purton riding Admire Rakti (centre). AP photo / Vince Caligiuri

The tragic deaths of the favourite Admire Rakti and seventh-placegetter Araldo soon after the Melbourne Cup have focused attention on the risks involved in racing horses.

Admire Rakti, from Japan, died from acute heart failure soon after the race, according to reports of a post-mortem examination.

Racing Victoria is now considering changes to the way horses are returned to the mounting yard after Araldo fractured a bone when he was "frightened" by a spectator who raised a flag. The fracture was not repairable and the horse was euthanised.

Horses are large and powerful animals with a sensitive and explosive flight response to perceived danger, which puts them by nature at risk of injury and even death whether they are racing or left alone in a paddock.

The high profile of horse racing means that injuries and deaths of racehorses on the track are in the public spotlight.

Horse racing in Australia (and New Zealand) is highly regulated and detailed data is collected for all adverse incidents on racetracks. This is used by researchers and racing authorities to track trends and investigate risk factors that may be modified.

The rate of sudden deaths on Victorian Thoroughbred racetracks over the past 10 years is 0.06 per 1000 flat race starts. This equates to one to two sudden deaths a year in Victoria. The rate of limb injuries in flat racing resulting in euthanasia on Victorian race tracks over the same period is 0.4 per 1000 starts.

Many limb injuries in racehorses can heal with time or be repaired with surgery but recovery depends on the severity of the injury. Complex fractures may not be repairable because horses need to be able to bear full weight on all four limbs immediately following surgery and this can be difficult or impossible to achieve.

All horses that die on metropolitan tracks in Victoria undergo a necropsy routinely. But even with a post mortem examination, discovering the cause of death can be challenging. It is possible to find the cause of death in about 50 per cent of cases but in the remainder the cause is unclear.

Commonly identified causes of sudden deaths include bleeding into the lungs -- exercise induced pulmonary haemorrhage -- and heart failure.

Bleeding into lungs occurs when the thin membrane separating the blood in the capillaries from the air in a lung's small air sacs ruptures.

This is thought to occur as a result of the extremely high pressure generated within the pulmonary capillaries in order to meet the muscles' demands for oxygenated blood during exercise. A small amount of haemorrhage has little effect on the horse but a large amount can have serious consequences.

It is for this reason that when blood is observed coming out of the nostrils, affected horses are excluded from racing.

Much less is known about the causes of heart failure in horses during racing. Although these events are often termed "heart attacks", they are likely to be quite different from heart attacks in people.

The nature of horses is such that anything we do with them is inherently risky, including racing. In Australia, the risks are relatively low but we need to strive to lower them even further. Every death of a racehorse is a tragedy, but one from which we need to learn.

Chris Whitton is associate professor of equine medicine and surgery at the University of Melbourne.