It truly takes a global disaster to throw the Kentucky Derby off its game. For only the second time in its 146-year history, the prestigious horse race has been postponed. The jewel of the Triple Crown was previously delayed for several months during World War II, but today, the culprit is the novel coronavirus pandemic.

Indeed, at tracks all across the nation, the horse-racing industry has taken the unprecedented and economically risky step to cancel races during a time when the sport is facing increased public scrutiny and opposition.

It’s a point that led to intense media attention in the spring of 2019 when a rash of thoroughbreds mysteriously lost their lives competing on California’s Santa Anita Park racetrack—where the famed Seabiscuit once galloped. Over a period of several months, 28 horses suffered serious injuries on the track that required euthanasia, most due to catastrophic leg fractures.

With no obvious explanation and tensions mounting, a team of researchers was called to investigate. Among them was Equine Research Hall of Fame inductee Susan Stover (’74, ’76 DVM), who is internationally known for her expertise in equine bone development, repetitive stress, and catastrophic injuries.

In 2008, Stover testified before the House Subcommittee on Commerce, Trade, and Consumer Protection in response to the tragic breakdowns of Kentucky Derby winner Barbaro, who shattered his leg in the Preakness, and Eight Belles whose valiant Derby run ended with two broken ankles.

“The Santa Anita situation was bad—we didn’t like it,” says Stover, distinguished professor and director of the J.D. Wheat Veterinary Orthopedic Research Laboratory at University of California, Davis. “Anytime we lose a single horse, it’s one too many.

“The racing industry is getting a wake-up call, which is an opportunity for change,” she says. “My goal is to enhance the safety of the horse and all those who work with the horse. If the welfare of the horse is our focus, the welfare of the industry will follow.”

Contrary to newspaper headlines, Stover says racehorse deaths have actually been declining for the last few years—up to thirty percent prior to the Santa Anita cluster.

“That’s a huge reduction,” she says. “We’re making headway but there’s room for improvement. The California racing industry has taken a lot of small steps that add up to a significant reduction in fatalities such as limiting the amount of painkillers horses are allowed, banning high toe grabs—or cleats—on horseshoes, and for a time, switching from dirt to synthetic track surfaces.”

Similar clusters of deaths have happened at other racetracks and Stover says they usually involve multiple factors.

“These injuries aren’t just a sudden step in a hole. It’s the result of what the horse has been doing for the previous two months,” she says.

At her laboratory, Stover collaborates with orthopedic surgeons and biomedical engineers to meticulously unravel the chain of events that can trigger these catastrophic injuries. Her team is also developing methods for early detection and prevention.

“We’ve found these injuries develop as mild injuries, most often as a stress fracture or remodeling in joints that temporarily weakens the bone and predisposes it to fracture,” she says.

“The tricky part, however, is determining which other risk factors are involved, things like hoof conformation and shoeing, drug use, how hard the racetrack surface is, and how intensely the horse is training. Sometimes risk factors come together all at once and you have a cluster of injuries, and that’s what happened at Santa Anita.”

For one, Stover says they had a spate of heavy rains which called for sealing the track.

“This makes the surface a little harder, so that every stride the horse takes causes a heavier impact on the bones,” she says.

“Also, the horses came from a different racetrack where they’d been training intensely. These fractures occur when there’s a lot of bone damage over a short period of time. The horse’s body is continually repairing this damage but when it exceeds the rate the body can heal, that’s when they get in trouble.”

Stover says the discovery that catastrophic injuries are the result of a chronic process opened the door for intervention.

“The most common cause for death is unrecoverable fetlock (ankle) injury and we’ve now pinpointed the pre-existing weak spot that allows these bones to fracture under otherwise normal circumstances,” she says.

Her team is using computer simulations to determine training and racing schedules that could help prevent such injuries.

“Essentially, we can model if a horse gallops this far today and that far tomorrow, how much bone damage will it cause?” Stover says. “And, is it something the body can heal, or does it get worse?

“Ideally, we want to prevent even mild injury. We want to increase racehorse longevity, and at the end of their career, have them be healthy enough to do something else.”


Stover received the Lifetime Excellence in Research Award from the American Veterinary Medical Association in 2016.