(CNN) - Just two days after racing resumed at Santa Anita Park, another horse died on the famed track Sunday, becoming the 23rd horse death since late December.
Racing at the Southern California park had only resumed Friday, after more than three weeks of closure.
After nearly two dozen horses died at Santa Anita Park since December 26, it closed to racing on March 5. In response to the spate of deaths, the park's owner, the Stronach Group announced rules that limited the use of whips and banned the use of nearly all medication on race day. After the changes were approved by the California Horse Racing Board, they went into effect when Santa Anita re-opened Friday.
But on Sunday, a race horse named Arms Runner fell and collided with another horse at the dirt crossing during the San Simeon Stakes. Arms Runner's injury was fatal. The other horse, La Sardane was not injured, according to a Santa Anita Park statement.
"While this incident happened during competition on a track that has been deemed by independent experts to be safe, we are working closely with the California Horse Racing Board (CHRB) to understand if there was anything additional that we could have done to prevent today's tragedy," according to the park's statement.
"Today's incident speaks to the larger issue of catastrophic injuries in horse racing that The Stronach Group together with our industry stakeholders are working to solve throughout California and across the country," it stated.
The deaths of nearly two dozen horses have been baffling. Many people connected with the park believe that rain has been a factor in the horses' deaths, but not all agree why. Southern California had its wettest winter in almost a decade.
Last month, the Los Angeles County district attorney's office assigned investigators to look into the horse deaths.
PETA said Sunday that the racing board, horse owners and trainers hadn't done enough.
"They did not take every measure needed to protect the horses," said Kathy Guillermo, PETA senior vice president in a statement. She pointed to the drug Lasix, a diuretic that is permitted at Santa Anita at lower than previous levels and will eventually be phased out.
"All drugs need to be banned entirely, and the known-safest racing surface -- a synthetic track -- must be used," Guillermo said.
She also called on California Governor Gavin Newsom to form an independent panel to investigate the training and veterinary practices in California racing.
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