The Thoroughbred racing industry is actively developing strategies to mitigate fatal catastrophic injuries. In 2009, The Jockey Club established the Equine Injury Database (EID) to evaluate injuries in Thoroughbred racehorses throughout the United States and Canada. In a retrospective cohort study, researchers examined fatal musculoskeletal injuries (MSI) between 2009-2023 to identify specific risk factors that contribute to such injuries.
EID Data on Racehorse Fatalities
At every sanctioned race, a veterinarian is required to submit a standardized form documenting pre- and post-race injuries to the EID. This form includes a “triage score” for every horse demonstrating lameness, limb deformity, or limb instability that makes them ineligible to race. To regain permission to race, the horse must undergo another veterinary examination.
From 2009-2023, the EID detailed 5,102,473 race starts of 324,407 horses at 163 racetracks in the U.S. and Canada. Only horses born after Jan. 1, 2007, were included in the database. Fatal musculoskeletal injury outcomes that occurred more than three days after race day were excluded from the study. Using the inclusion criteria, the cohort study included 3,851,659 race starts of 250,940 horses at 115 racetracks.
“The case definition used was any racing MSI resulting in either death or euthanasia, with fatality being recorded within 3 days of race day,” the study authors explained. The final study cohort included 5,733 fatal MSI cases; the other 3 million horses served as controls.
In this study, there were 1.49 fatalities per 1,000 race starts:
- 92.9% on race day.
- 4.2% the day after racing.
- 1.7% two days after racing.
- 1.2% three days after racing.
Risk Factors for Fatal MSI in Racehorses
The researchers identified 97 potential risk factors, but only 20 were statistically significant in the final multivariable model. Increased odds of fatal MSI were associated with:
- Starts on turf, dirt, or off dirt (any condition other than fast) surfaces compared to synthetic surfaces increased risk by 1.57 times.
- Larger numbers of starters, especially more than 10 horses in a field, increased risk by 1.06 times compared to fields of seven or fewer horses.
- Starts over shorter distances increased risk by 1.06 times compared to distances longer than 6 furlongs.
- High purse sizes ≥ $100,000 increased the risk 1.37 times compared to purses ≤ $20,000.
- Races with no void claim rules had increased risk of fatal MSI. In contrast, the strictest void claim rule had the lowest odds ratio of 0.76. (The void claim rule “deters owners from entering horses with known pathology into races.”)
- Horses raced as claimers were at increased risk of fatal MSI, especially if claim prizes were less than $10,000. Horses may go into claiming races for a number of reasons, including underlying pathology known or unknown to the owner. A lower purse might indicate high motivation by the owner to sell the horse even at a low price.
- Older horses ≥ 5 years of age increased risk by 1.32 times compared to those ≤ 3 years.
- Horses that first raced at 3 years of age or older had a 1.14-times increased risk of fatal MSI compared to horses that first raced at age 2.
- Geldings and stallions had an increased risk of 1.56 times compared to mares.
- Race starts within 30 days of a previous start accounted for 60% of the fatalities from MSI. Each additional race start within the previous six months further increased the risk of fatal MSI.
- Odds of fatal MSI increased with each additional week between the previous training workout and a race compared to race starts within seven days of a workout. Recent exercise is protective, whereas excess exercise over a sustained period might increase fatal MSI risk.
- Changing to a new trainer in the first two race starts increased odds of fatal MSI by 1.18 times.
- Horses considered competitive based on betting odds had a higher risk of fatal MSI.
- Horses with more placings in their careers had a lower risk of fatal MSI. The authors noted that more placings might indicate a “healthy horse effect” that enables the horse to continue racing for a longer career. Improved success was seen in horses with more total place results in their career, especially eight or more career placings compared to horses with one or fewer placings.
- Any triage score in the horse’s career increased odds by 1.55 times compared to horses that were never cited on a Veterinarian’s List. The closer in time the horse was released from the Vet List, the greater the risk of a fatal MSI despite “passing” a veterinary exam. A horse on the Vet List might experience a fatal MSI months or even years later. By acknowledging this risk, horses with a previous triage score could undergo more diagnostic testing and increased veterinary scrutiny during prerace examinations.
Final Thoughts
It is important to note that records of veterinary management during training, racing, and layoff time are not part of the EID information used to develop the risk models. In addition, there is limited training and veterinary history prior to the sale of a horse to begin its racing career.
The report also mentions that race-day phenylbutazone is associated with increased fatality odds in South American racing and race-day furosemide is associated with increased odds of sudden death in North America.
The objective for scrutinizing these risk factors is to proactively identify horses at risk before race day and to make concerted efforts to mitigate those risks.
Reference
Bennet ED, Parkin TDH. Novel risk factors associated with fatal musculoskeletal injury in Thoroughbreds in North American racing (2009 – 2023). Equine Veterinary Journal Mar 2025; DOI: 10.1111/evj.14503
Related Reading
- Update: Thoroughbred Racehorse Safety Initiatives
- Exercise-Associated Sudden Death in Horses
- EVJ Highlights Ongoing Work to Improve Racehorse Safety
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