A two-horse spill in the San Simeon Stakes at Santa Anita has led to the 23rd equine fatality at the Southern California track in just over three months.

Arms Runner injured his right front leg and fell in the Grade Three race on turf on Sunday, two days after Santa Anita reopened for racing after being closed for nearly a month.

The fall caused a trailing horse, La Sardane, to fall. The mare got back on her feet and walked back to her barn under her own power. She did not sustain any injuries, according to a statement issued by the track.

Arms Runner was tended to by track veterinarians and laster euthanised.

The accident occurred as the horses crossed the dirt surface during the transition from the hillside turf course to the main turf course.

The majority of the fatalities at the Arcadia track since December 26 have occurred on the main dirt surface.

"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 to understand if there was anything additional that we could have done to prevent today's tragedy," a statement from the track said.

"The 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."

The track was closed on March 3 so officials could inspect and renovate the dirt surface after the series of fatalities that have drawn national attention outside the sport and criticism from animal rights groups.

Track officials have not announced a singular cause for the unusual number of deaths.

The Stronach Group, which owns Santa Anita, announced an immediate reduction in the amount of anti-bleeding medication Lasix allowed on race days. The California Horse Racing Board approved the measure and it took effect on Friday.

A proposed rule that would eliminate the use of whips, except in cases where a horse's or jockey's safety is involved, still requires the approval of various state agencies.