Research: First Study of Sudden Death in Racehorses Reveals That Cause of Death is Unknown in Half of Cases

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Both racehorses and sport horses are susceptible to sudden death, usually during or after exercise or competition. While few statistics are available about sport horses, a Scottish research group collected data from sudden death cases in racehorses in several countries. (Photo by Tsutomu Takasu)

Both racehorses and sport horses are susceptible to sudden death, usually during or after exercise or competition. While few statistics are available about sport horses, a Scottish research group collected data from sudden death cases in racehorses in several countries. (Photo by Tsutomu Takasu)

Research at the Royal (Dick) School of Veterinary Studies at the University of Edinburgh in Scotland is yielding some clues regarding the provenance and risk factors for sudden death in racehorses.

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The Horserace Betting Levy Board in Great Britain funded a three-year scholarship at the Dick Vet in an attempt to gain a better understanding and find ways to reduce the likelihood of this devastating, but thankfully extremely rare, occurrence.

Sudden equine death is extremely challenging to investigate as it is, by definition, any fatality which occurs in a closely observed and previously healthy horse, during or immediately after exercise. The belief leading to this study has been that if the risk factors could be identified, it would be possible to reduce the likelihood of sudden death occurring.

The HBLB’s pioneering scholarship was filled by veterinarian Catriona Lyle, who studied at the University of Edinburgh’s Royal (Dick) School of Veterinary Studies with Professor Bruce McGorum, Dr Lisa Boden and Dr Tim Parkin.

During Catriona’s three-year scholarship she coordinated a collaborative study involving information from racetracks in North America, Australia, Japan and Hong Kong. She studied post-mortem data from 284 cases that had died across a 20-year period.

In the UK, post-mortems are not always carried out in cases of sudden death and so gaining access to international records was essential to the project.

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“The study has shown that the cause of death can be quite variable, ranging from severe lung bleeding to a pelvic fracture that causes massive bleeding into the abdomen. But in approximately half the cases I studied, the pathologist was uncertain as to the cause of death. The most likely explanation for death in these situations is cardiac rhythm irregularities, but this is very difficult to prove,” says Catriona Lyle.

Research veterinarian Catriona Lyle

Research veterinarian Catriona Lyle

Following Catriona’s analysis of these international data, she looked exclusively at cases of sudden death in British racehorses. Over a seven year period, based on over 700,000 race starts, there were 201 sudden deaths on British racetracks.

The same syndrome is known to occur in eventing, show jumping and foxhunting, but statistics have not been established in these sports.

There have been estimates that in the general horse population around five percent of horses in the same age range as racehorses die each year because of illness or injury. Cardiac disease accounts for about five percent of these deaths and older horses in the general population are more prone to cardiovascular-related death.

Key Facts from the study

  • This was a major study into death on racetracks in the United Kingdom.
  • British Horseracing Authority records of 705,914 race starts from January 1, 2000 to December 31, 2007 were reviewed.
  • The problem of sudden death in racehorsese in the United Kingdom is extremely rare.
  • There were 201 cases of sudden death associated with racing.
  • Horses running in the National Hunt (jump) races were more at risk for sudden death than those in flat races.
  • Horses that had raced within the last 60 days were less likely to be affected.
  • Identification of risk factors may help to reduce the risk of sudden death in the future.

In summary, the British part of the sudden death study revealed that: 1) increasing age is a risk factor, 2) steeplechases posed more of a risk than flat races and 3) racing during the summer was associated with a greater risk of sudden death. However, Lyle stressed, this should be put in the context that, on average, steeplechasers are also older than hurdlers or flat horses.

Jenny Hall (British Horseracing Authority photo)

Jenny Hall (British Horseracing Authority photo)

Jenny Hall, chief veterinary officer of the British Horseracing Authority, welcomed Catriona’s findings. She commented, “This was an extremely useful project. We are continuing to build on Catriona’s research with an ongoing investigation currently running at Britain’s northern racetracks. Sudden death is very distressing and we hope that owners will understand that allowing a full investigation into every racecourse death will help us reduce this risk.”

To learn more:
Lyle CH, Uzal FA, McGorum BC, Aida H, Blissitt KJ, Case JT, Charles JA, Gardner I, Horodagoda N, Kusano K, Lam K, Pack JD, Parkin TD, Slocombe RF, Stewart BD, Boden LA (2011) Sudden death in racing Thoroughbred horses: an international multicentre study of post mortem findings. Equine Vet J 43 324-331.

Lyle C, Blissitt K, Kennedy N, McGorum BC, Newton R, Parkin T, Stirk A, Boden L (2012) Risk factors for race-associated sudden death in Thoroughbred racehorses in the UK (2000-2007). Equine Vet J 44 459-465. DOI: 10.1111/j.2042-3306.2011.00496.x.

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