Maria Borell, the trainer who guided Runhappy to victory in the $1.5 million Breeders' Cup Sprint at Keeneland on Saturday, was removed from the horse's care the next day.
"Just went from the best day of my life to the worst day of my life," Borell posted on Twitter on Sunday. "My heart is in a million pieces."
Borell's post suggested her firing was the result of a disagreement over Runhappy's care that took place Sunday morning.
Laura Wohlers, the racing manager for Runhappy's owner, James McIngvale, confirmed to the Blood-Horse the decision to change trainers but said it had nothing to do with a disagreement with Borell.
Borell's Twitter post said Runhappy had heat in an ankle the morning after the race but Wohlers wanted to send him to the track.
Wohlers told the Blood-Horse they always jog Runhappy after races and that a vet found no problems Sunday morning.
Borell — a 32-year-old native of Syracuse, N.Y., who was saddling her first Breeders' Cup competitor — operates 120-acre Beacon Hill Farm near Lexington.
McIngvale praised Borell's work after the race Saturday.
"Maria has done a great job with the horse ever since we brought him here to Kentucky at the Kentucky Training Center. Success is measured by results and results are pretty good."
McIngvale's daughter, Laura McIngvale Brown, told the Blood-Horse on Sunday, "We really respect Maria. We think she's done a great job, but unfortunately it was time for us, as a team, to move forward."