Sudden Equine Death Research yields clues

The Dick Vet has long been on the forefront of equine research and has a proud history of working with partners across the industry. Recently, the Horserace Betting Levy Board funded a three year scholarship at the Dick Vet, to take the lead in a multi-centre study of sudden death in racehorses , 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 in a previously healthy horse, during or immediately after exercise. The belief, leading to this study, has been that if the risk factors could be identified, this could help to reduce the likelihood of sudden death occurring. The HBLB funded this pioneering study by awarding a scholarship to vet Catriona Lyle, who studied at the University of Edinburgh’s Royal (Dick) School of Veterinary Studies with Professor Bruce McGorum, Head of Equine Sciences, Dr Lisa Boden and Dr Tim Parkin.

During Catriona’s three-year scholarship she coordinated a collaborative study involving information from racecourses in North America, Australia, Japan and Hong Kong, studying post-mortem data from 284 cases 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 these international records was essential.

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.

Catriona Lyle

Following Catriona’s analysis of these international data she then looked at cases of sudden death in British Racehorses. Over a seven year period, with over seven hundred thousand race starts, there were 201 sudden deaths on British racecourses. The same syndrome is known to occur in eventing, show jumping and hunting but statistics have not been established in these sports.

There have been estimates that in the general horse population around 5% of horses in the same age range as racehorses die each year because of illness or injury. Cardiac disease accounts for about 5% of these deaths and older horses in the general population are more prone to cardiovascular related death.

In the UK sudden death study, Catriona found that increasing age is a risk factor, steeplechases posed more of a risk than flat races and racing during the summer was associated with a greater risk of sudden death. However, this should be put in the context that, on average, steeplechasers are older than hurdlers or Flat horses.

Jenny Hall, chief veterinary officer of the British Horseracing Authority, welcomed Catriona’s findings.

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.

Jenny Hall

The research was also welcomed by Professor Willie Donachie, Chairman of the HBLB’s veterinary advisory committee.

Not only did she complete two major studies on sudden death where her results will pave the way to reducing this problem but she also passed her European Diploma exam; a fantastic set of achievements in only three years

Professor Willie Donachie

Key Facts from the study

• This was a major study into death on UK racecourses
• British Horseracing Authority records of 705,914 race starts from 1st January 2000 to 31 December 2007 were reviewed
• The problem is extremely rare
• There were 201 cases of sudden death associated with racing
• Horses running in the National Hunt 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 these risk factors may help towards reducing the risk of sudden death in the future

Publications arising from the study;

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.