Trainers urged to focus on changes to bone to avoid catastrophic injuries

LEXINGTON, Ky. – Trainers of racehorses should focus on the adaptive changes to bone that occur in response to exercise in order to avoid catastrophic injuries, with a particular focus on those changes that occur when a horse has been returned to training after a long layoff or in older horses that have undergone high levels of training for a prolonged time, according to Dr. Sue Stover, a University of California-Davis professor who is one of the most foremost experts on musculoskeletal injuries in horses.

Stover, appearing on a webinar Tuesday afternoon that was organized by the Grayson-Jockey Club, presented study results and bone scans to drive home a point that she said was critical to the maintenance of good bone health – the proper recognition of how a horse’s skeleton is responding to new stresses, so that stressed bone is given an adequate resting opportunity to remodel before new stresses are applied to the bone.

Data from Stover’s work, which include the administration of California’s necropsy program for racehorses since 1990, show that bone not only remodels effectively if given rest periods, but that the resulting bone is stronger than before it became stressed. But without proper recovery periods, bone can instead weaken, which can lead to a downward spiral of degeneration that leads to catastrophic injuries.

“If we breeze that horse for the first time, and it gets a little bit of damage, and then we load it too soon, before the bone has recovered, we get more damage,” Stover said. “And if we do it again and again, we get a little more damage, and the bone is a little weaker because it can’t take what we give it. . . . That is the path to injury.”

Catastrophic injuries have become a much more critical issue of concern in U.S. racing after dozens of horses suffered fatal injuries in California at the beginning of last year in a short period of time, leading to prolonged and intense criticism of racing nationwide. The breakdowns have led a number of racing jurisdictions to implement stricter medication rules and stronger veterinary oversight of horse populations.

Stover was the first researcher to definitely show that pre-existing injuries to bone are the most significant factor in catastrophic injuries, and her work disproved the “bad step” theory in U.S. racing, which held that catastrophic injuries occur as the result of a single overload of bone. Instead, Stover’s work concluded that the site of a fracture occurs at a place where the bone has already been weakened. In addition, her work concluded that fracture sites occur at predictable places in certain bones.

That research has been critical to the jobs of regulatory veterinarians, according to Dr. Jennifer Durenberger, a former regulatory veterinarian who has conducted thousands of pre-race examinations of horses. (Durenberger is now the Jockey Club steward at the New York Racing Association racetracks.)

Durenberger said on the webinar that Stover’s work has guided regulatory vets to the spots where injuries are most liable to occur, a trend that has evolved conspicuously over her career.

“I can’t think of anything that has more changed my inspections other than the information that has come out of these [necropsy] programs,” Durenberger said. “We do now know these predictive areas. We have the horse’s history. We know what the horse has been doing. . . . And so we can focus our exams and spend more time in those areas where we might expect to see more of these injuries.”

Stover said that new bone-scanning technology, such as positron emission tomography, or PET scans, have shown promise as a new diagnostic tool in identifying weak areas of bones and lesions. Santa Anita, where the 2019 catastrophic injuries occurred, has recently put a PET scanner in place, in the hopes that the scanner might reduce injuries in the future.

But Stover also cautioned that there is a high degree in variability among racehorses that might show problem areas in a PET scan. New scanning technologies also were a subject of a previous webinar this year by the Grayson-Jockey Club, which had to cancel its Health and Safety of the Racehorse Summit this year to the COVID-19 pandemic. Participants in that webinar also cautioned about the limitations of new scanning technology.

Stover said that the new PET scanning technology is “exciting.”

“But we have to be cautious,” she said. “It gives us a third dimension, it allows us to pinpoint [problem areas]. But we also are learning very quickly that some horses respond very well and that some of these lesions can be resolved faster than we anticipated.”

What is the answer to determining when problems illuminated by a scan require different training schedules or a lay-up, Stover was asked.

“Horsemanship, horsemanship, horsemanship,” she answered.

Durenberger said that she is hopeful that the U.S. racing industry can reduce catastrophic injuries by the new measures being put in place at racetracks that require more monitoring of racehorse populations as they go about their daily routines of training and racing, and from the knowledge being gained by the data and research produced by programs like Stover’s.

“It’s a pretty amazing thing, this culture of data,” she said.