Trainer Saffie Joseph Jr has been suspended after two of his horses died in the lead-up to Saturday's 149th Kentucky Derby.
Parents Pride and Chasing Artie collapsed and died at the Churchill Downs track, with the cause of death still unknown.
Another of Joseph Jr's horses, Lord Miles, has been scratched from the race following his suspension.
Four horses have now died in the build-up to America's most celebrated race.
The suspension prohibits Joseph Jr, or any trainer directly or indirectly employed by him, from entering horses in races or applying for stall occupancy at all Churchill Downs Incorporated (CDI) owned racetracks.
"Given the unexplained sudden deaths, we have reasonable concerns about the condition of his horses and decided to suspend him indefinitely until details are analysed and understood," said Bill Mudd, the CDI president and chief operating officer.
"The safety of our equine and human athletes and integrity of our sport is our highest priority. We feel these measures are our duty and responsibility."
Take Charge Briana and Wild On Ice, trained by Wayne Lukas and Joel Marr respectively, both had to be put down down after suffering leg injuries at the track in Louisville earlier this week.
CDI says it is working with regulators to investigate the circumstances behind the deaths.
An earlier CDI statement prior to Joseph Jr's suspension described the deaths as "completely unacceptable" and that "these troubling incidents are alarming and must be addressed."
Practical Move has also been removed from the 20-strong field due to an elevated temperature.
The Kentucky Derby, which has been held uninterrupted since 1875, is the first of US flat racing's annual Triple Crown treble, that also includes the Preakness Stakes in Baltimore and Belmont Stakes in New York.
ncG1vNJzZmivp6x7o67CZ5qopV%2BovbC%2B02ifqKqjmnqzrcKipaBnZmqBen6Samk%3D