What We’re Learning From Horse Racing Research

Researchers worldwide are examining ways to prevent injuries in racehorses; their findings could help prevent issues in sport horses, as well

When a racehorse suffers a catastrophic injury in a high-profile race, the industry makes headlines … for all the wrong reasons. In recent decades mainstream media has shone a spotlight on racing injuries, and industry organizations have poured thousands of dollars into investigating why they occur. As a result, we know a lot about the forces placed on these elite athletes’ bodies.

Much of the research has revolved around identifying risk factors for and ways to prevent catastrophic injuries and fatalities. Here, several university researchers from North America and abroad share recently published and ongoing studies on this topic, along with their potential impact on racehorse and sport horse health down the road.

Identifying Early Warning Signs

Preventing injuries is important not only for racehorse health but also jockey safety and public perception, says David Horohov, PhD, chair of the University of Kentucky’s (UK) Department of Veterinary Science and director of the Gluck Equine Research Center, in Lexington. He and his colleagues have been working on a series of studies investigating injury prevention.

An assembled group including James MacLeod, VMD, PhD, and Jennifer Janes, DVM, PhD, Dipl. ACVP, of the Gluck Center; Laura Kennedy, DVM, Dipl. ACVP, of the UK Veterinary Diagnostic Laboratory; and Mary Scollay, DVM, of the Kentucky Horse Racing Commission, are evaluating injury risks and possible precursors.

Horohov says their research thus far suggests that orthopedic injuries in racehorses are related to long-term effects rather than acute events. “It’s a chronic injury pattern that eventually leads to an acute failure,” he says.

In addition, Horohov and colleagues, including UK’s Allen Page, DVM, PhD, are looking at whether inflammatory changes that occur in racehorses and sport horses indicate a pathologic (causing disease or damage) condition is brewing.

As bones and muscles experience stress during exercise, they undergo microdamage as part of their normal adaptive process. Ideally, this process helps strengthen both bone and muscle. However, if the horse is overtrained or does not adapt well to training, the result is inflammation and potential injury. Horohov and Page have hypothesized that bloodwork should reveal certain inflammatory marker patterns that indicate systemic inflammation caused by early microlesions.

“Some microlesion formation is likely part of the normal remodeling effort,” Horohov says. “It is when the destructive aspect of lesion formation gets ahead of the repair process that the inflammatory response becomes exaggerated, leading to systemic inflammation … thus, the tipping point where inflammation does more harm than good.”

The team has already examined bloodwork of 2-year-old racehorses and older racehorses in training, along with racehorses working on treadmills. They’re now gathering data from endurance horses, jumpers, and dressage horses to look for similar patterns in those ­populations.

Horohov says the underlying goal is to identify horses with abnormal expressions of inflammatory responses so trainers can back down a horse’s training as needed to prevent him from becoming predisposed to or developing an injury.

Another important population this team has studied is racehorses rehabilitating from injury. Their goal is to identify inflammatory markers to help trainers determine the rate at which they can safely bring horses back into training and how much training a horse can tolerate.

Identifying Fatality Risk Factors

Some racing and training injuries are so catastrophic that they result in death or euthanasia. In a retrospective study led by Peter Physick-Sheard, BVSc, Dipl. VetSurg, MSc, FRCVS, at the University of Guelph¹, in Ontario, researchers analyzed racehorse deaths logged with the Ontario Racehorse Death Registry from 2003 to 2015 that occurred within 60 days of a race or trial entry (timed workouts and Standardbred qualifying races).

The researchers examined differences between racing Thoroughbreds, Standardbreds, and Quarter Horses as they related to age, sex, and circumstances of death, such as time and location, suggested cause, and whether it was an exercise-­associated mortality (EAM) or non-­exercise-associated mortality (NEAM).

The mean combined EAM and NEAM mortality rate was highest for Thoroughbreds (2.93 deaths per 1,000 starts), which was 4.6 times higher than that of Standardbreds (0.63/1,000 starts). Quarter Horses landed in the middle (2.08/1,000 starts). Thoroughbred mean annual EAM was 8.1 times that of ­Standardbreds.

Physick-Sheard’s team said their most notable finding was that Thoroughbred mortality was highest in young, intact male horses. In Thoroughbreds and Quarter Horses, mortality rates of all sexes were higher at age 2 than any other.

Researchers noted a higher mortality rate across all breeds for younger horses (possibly due to skeletal immaturity and a propensity toward fatigue) and older horses (possibly due to cumulative damage). The mortality risk among middle-aged horses was lower. Basically, says Physick-Sheard, mortality rate followed a curve, falling over the first two to three years, then increasing. Groups were aged by year, for Thoroughbreds, from 2 to 10.

When looking at cause of death, “musculoskeletal injury, including breakdowns, fractures, dislocations, and tendon ruptures, was the largest category,” said the authors. Thoroughbreds experienced musculoskeletal injuries 8.59 times more than Standardbreds.

The second-most-common cause was collapsing for no reason and sudden death. Colic; medical problems (e.g., bacterial infections, septicemia, kidney disease, etc.); iatrogenic problems (those inadvertently caused by treatment); and accidents of any kind (including necks and pelvises fractured in falls) followed.

“Breed differences in mortality provide pointers toward management strategies that could reduce mortality, enhance welfare, increase longevity, and reduce costs of participation,” wrote the study authors. “Exercise-associated mortality, in particular, is clearly related to the nature and intensity of competition undertaken by the different breeds and may reflect the time different industries allow for preparation of young athletes.”

In the U.K., Sarah Rosanowski, PhD, PGDipl. VCS, and colleagues evaluated risk factors for race-day fatalities in flat racing (not jumping obstacles) Thoroughbreds in Great Britain from 2000 to 2013 as part of her postdoctoral research at the Royal Veterinary College.² She’s currently an assistant professor in ­evidence-based veterinary medicine for the Centre for Applied One Health Research and Policy Advice at the City University of Hong Kong’s Jockey Club College of Veterinary Medicine and Life Sciences.

The study included 806,764 race starts, 548,571 of which were on the turf. Out of 610 fatalities, 377 (61.8%) occurred on the turf. The incidence of race-day fatality during all flat racing was 0.76 per 1,000 starts, with 0.69 per 1,000 starts on turf and 0.90 per 1,000 starts on all-­weather (synthetic) surfaces. This indicates that all-weather surfaces increase fatality risk, says ­Rosanowski, compared to turf.

Her team divided fatality causes into three categories:

• Musculoskeletal injuries (88.8%);
• Nonmusculoskeletal injuries (10.3%); and
• Related to both (0.9%).

Of musculoskeletal-injury-related deaths, 75.5% were due to fractures, with tendon or ligament injuries, fetlock dislocation, and multiple injuries accounting for the rest.

Of nonmusculoskeletal-injury-related deaths, 8.6% were due to vascular catastrophe (any terminal event of vascular origin, such as cardiac issues or ruptured aortas); sudden death due to this cause is rare compared to musculoskeletal injury, says Rosanowski. They attributed a small proportion of deaths to epistaxis (­bleeding from the nostrils), lacerations, other soft tissue injuries, or multiple causes. 

Risk factors on both turf and all-­weather tracks included a firmer (turf) or faster (all-weather) racing surface, longer race distance, wearing an eye cover such as blinkers for the first time, increased age, racing in autumn or summer, horses in their first year of racing, and high average performance scores (better-­performing horses). An increased number of starts reduced a horse’s odds of fatality.

Auction races (restricted to 2- or 3-year-olds bought or sold at certain public auctions) had 1.46 times the odds of fatality as other race types. Turf horses running in Group 1 races (the highest-level stakes race) were 3.19 times more at risk.

Rosanowski’s team published a 2017 study³ using the same data set that showed epistaxis incidence was 1.59 per 1,000 starts on all-weather surfaces. Faster (firmer) going increased a horse’s odds of epistaxis and distal (lower) limb fracture but not fatality. Longer race distance increased the odds of fatality but reduced the odds of epistaxis. The odds of distal limb fracture increased with firmer surfaces, with more than 14 runners in a race, with increased horse age at first start, in better-­performing horses, and in horses that raced eight to 93 days previously. Horses from trainers with higher win percentages on all-weather surfaces were at increased odds of fracture, as well.

Preventing Catastrophic Injuries

Researchers at the University of California, Davis, (UC Davis) have been studying racehorses in various capacities, particularly their injury risk, for decades.

“Because 80% of racehorse deaths are due to catastrophic injuries, focus on factors that affect injury risk should be a high priority,” says Susan Stover, DVM, PhD, Dipl. ACVS, director of the UC Davis J.D. Wheat Veterinary Research Laboratory. “Because the causes of injury are multifactorial, a several-pronged approach is needed,” including racing surfaces, hoof management and shoeing, and training schedules.

She says her team’s most recent impactful findings include using ultrasound to detect humeral (the bone between the shoulder and elbow joints) stress fractures in racehorses (TheHorse.com/167901) and positron emission tomography (PET scan) to detect pre-­existing issues that could lead to catastrophic fetlock injuries.

In a 2018 study4 UC Davis researchers compared the use of PET scans with F-sodium fluoride (F-NaF, which serves as a tracer to detect changes in bone) to other methods of diagnosing bone-stress-­related fetlock injuries, in hopes of preventing catastrophic injury. They found that PET scans with F-NaF picked up more bone lesions than nuclear scintigraphy (bone scan), computed tomography (CT), standing magnetic resonance imaging (MRI), and histologic (microscopic) examination. They concluded that a combination of PET with CT is important for localizing these lesions because PET findings reflect the tissues’ metabolic activity and CT provides the activity’s anatomic location.

RELATED CONTENT: PET Scan Research Could Improve Racehorse Safety, Welfare

“Consequently, PET has particular advantages for imaging the fetlock in racehorses because of its usefulness for not only detecting but also discriminating between metacarpal condylar (the distal cannon bone) and proximal sesamoid (in the fetlock hinge joint) bone abnormalities,” said the study authors.

“California has made several changes to the industry that stemmed from UC Davis research and have contributed to an overall reduction in injuries in racehorses,” says Stover. “The first key discovery was the recognition that catastrophic bone fractures were the acute manifestation of more chronic (pre-existing) stress fractures.”

Because the fetlock is the most common site of musculoskeletal injury in racehorses and the leading cause of fatalities in the U.S., UC Davis researchers have focused on the relationship between race surface hardness and fetlock injury risk. This has led tracks to harrow (drag) racing surfaces more frequently during training sessions to help prevent injuries.

Using computer simulations, UC Davis researchers also recently looked at race surfaces’ effects on fetlock motion during the stride’s stance phase (when the foot is in contact with the ground).5 They found that, basically, providing sufficient cushion material on top of the surface’s harder base can help prevent abnormal fetlock motion and reduce injury risk.

The team concluded that harrowing depth and frequency can influence limb motion significantly. They said computer simulations can give researchers more information on how race surface design and maintenance might reduce injury risk.

Stover says future UC Davis studies will focus on sesamoid bone fracture causes in racehorses, hard arena surface effects on the extended trot in dressage horses, economical ways to detect humeral stress fractures using ultrasound, and arena surface property effects on show jumpers.

Take-Home Message

This is just a small sampling of the research involving racehorses around the world. As scientists reveal more information about and ways to preserve racehorse health, their findings can translate to athletic horses of all types. Some are even leading to follow-up studies involving sport horses specifically.

These studies might be “of even greater importance to the sport horse due to … the fact that you’re expecting years of performance out of that animal,” says Horohov. “The ability … to both prevent as well as overcome injury is critical to the long-term health of that horse and the program it’s involved in.”

References

1. Physick-Sheard PW, et al. (2019). Ontario Racehorse Death Registry, 2003-2015; Descriptive analysis and rates of mortality. Equine Veterinary Journal, 51:64-76.

2. Rosanowski SM, et al. (2018). Risk factors for a race-day fatality in flat racing Thoroughbreds in Great Britain (2000 to 2013). PLoS ONE 13(3): e0194299.

3. Rosanowski SM, et al. (2017). Risk factors for race-day fatality, distal limb fracture, and epistaxis in Thoroughbred racing on all-weather surfaces in Great Britain (2000 to 2013). Journal of Preventive Veterinary Medicine, 148:58-65.

4. Spriet M, et al. (2018). F-sodium fluoride positron emission tomography of the racing Thoroughbred fetlock: Validation and comparison with other imaging modalities in nine horses. Equine Veterinary Journal, 0:1-9.

5. Symons JE, et al. (2017). Modelling the effect of race surface and racehorse limb parameters on in silico fetlock motion and propensity for injury. Equine Veterinary Journal, 49:681-687.