Some 29 horses have died at the Santa Anita track near Los Angles since Christmas, two of them last weekend, one of a broken hip and one of an apparent heart attack, the Los Angeles Times and other media reported.
Arcadia voluntarily closed for weeks in March after a spate of racehorse deaths, most of them due to injuries. Following an inquiry by the Los Angeles County District Attorney's Office, the track re-opened after pledging to implement safety reforms.
Stronach said in a statement on Wednesday that a new five-member review team including veterinarians and stewards would have the authority to scratch any horse off the racing rolls if it appears unfit.
"Every member of the review team must agree that the horse is not at an elevated risk of injury in order to clear a horse to race," it said.
"Horse and rider safety is our top priority at Santa Anita Park, and we remain steadfast in our commitment to making California horse racing the safest and best in the world."
Gov. Newsom on Tuesday urged the CHRB, which regulates horse racing in the state, to stop the races until it can make sure the racing is safe.
"I continue to be troubled by the horse deaths at Santa Anita Park," he said in a statement. "Enough is enough."
However, the CHRB does not have the authority to immediately close the race track at Arcadia. To do so, it must go through a formal process that includes a hearing with a 10-day notice period.
Santa Anita Park is slated to host the 2019 Breeders' Cup races in November.
(Reporting by Rich McKay; Editing by Gareth Jones)
