The filly was being led out of the barn at about 6 a.m. when something spooked her, causing her to flip over and fall on the 58-year-old exercise rider, according to publicity manager Tom Farrell.
The horse did not appear to have been injured.
"It's a tragic accident," Farrell said. "It's very sad." The racetrack is located at 1100 Eastshore Highway just off Interstate Highway 80 and Interstate Highway 580.