Churchill Downs is working with regulators after four horses died in the lead-up to the 1-1/4-mile race, including one that was entered to run in the first leg of thoroughbred racing's Triple Crown, Wild on Ice.
Joseph's horses, Parents Pride and Chasing Artie, died suddenly on Saturday and Tuesday, respectively.
"Given the unexplained sudden deaths, we have reasonable concerns about the condition of his horses and decided to suspend him indefinitely until details are analyzed and understood," Bill Mudd, the president and chief operating officer of Churchill Downs Incorporated, said in a statement.
Lord Miles was the second scratch announced for the derby on Thursday as Practical Move was also removed from the field due to an elevated temperature.
Cyclone Mischief, a bay colt trained by Dale Romans, will now enter the competition in the No. 20 post position following third-place finishes behind champion Forte in the Fountain of Youth (G2) and Florida Derby (G1).
A jockey for Cyclone Mischief has not yet been confirmed.
Also joining in the No. 22 spot is Mandarin Hero, who took second in the Santa Anita Derby last month. The dark brown colt is the second horse from Japan in this year's field along with Derma Sotogake.
