Over the course of the three races at this year’s Triple Crown, the odds are 10 to 1 that at least one horse will suffer a career-ending injury. “Orthopedically, the horse is a disaster waiting to happen,” says veterinarian Bob Harman. “They’re so big--a 1,000-pound animal on little toothpick legs--and they’re working at high capacity.” Harman is also the CEO of Vet-Stem, a California company that treats racehorses with stem-cell therapy. Since he founded Vet-Stem in 2002, his company has treated 4,141 horses for soft-tissue injuries such as tendinitis and muscle contusions, and he says 70 to 80 percent have healed completely.

Doctors generally reserve stem-cell therapy, which draws on those cells’ unique ability to regenerate and form into nearly any tissue, for patients with major medical problems, such as cancer and spinal-cord injuries. But veterinarians are “in a unique position to try stem-cell treatments for quality-of-life problems,” says Thomas Koch of the University of Guelph’s Ontario Veterinary College. Koch concedes, though, that there are many unanswered questions about veterinary stem-cell treatments, that the science isn’t fully understood, and that companies like Vet-Stem are working ahead of the evidence. “There is a demand from animal owners,” he says, because “what has been available wasn’t working very well.”

Frisbie’s tests build on other encouraging results. In 2007, Italian researchers published a study of two groups of horses with tendinitis. Among the 11 horses that received stem-cell injections and returned to racing, nine remained injury-free a year later. Of the 15 control horses that received a more conventional course of rehab, all reinjured themselves within a year.

Veterinarian Sean Owens, director of the two-year-old Regenerative Medicine Laboratory at the University of California at Davis, is performing his own, very specific, set of stem-cell rehab trials on horses, modeled after what tests on humans might look like. “Our clinical trials are proof-of-concept that researchers working on human stem cells can cite,” Owens says, adding, “so we can move toward trials on humans.”