It was the second deadly blaze this year at Riverside Downs in western Kentucky, near the Indiana border. Among the horses killed was Kept Lady, which won a race Sunday at Churchill Downs.
Investigators did not know what caused the blaze, which started between 5 and 5:30 a.m. EDT.
"It's just a terrible thing," said Jack Hancock, a manager at Riverside, which is now used to stable and exercise horses. "The worst thing a horseman could ever hear is the word 'fire."'
Five of the 31 horses in the barn that caught fire survived, but one was later euthanized. About 70 horses remain at the stables.
"It's just a tragedy that you don't want to get a phone call about," said Kenny Miller, owner-trainer of Kept Lady and another horse killed.
It was the second deadly fire this year at the former quarterhorse and harness track. Six horses died Jan. 4 in a fire blamed on a vending machine electrical cord.