That caused a trailing horse, La Sardane, to fall. The 5-year-old mare got back on her feet and didn't appear to sustain any injuries. Jockey Ruben Fuentes didn't ride the rest of the day.
Arms Runner was tended to by track veterinarians and vanned off. Track stewards said the horse was euthanized.
The accident occurred as the horses crossed the dirt surface during the transition from the hillside turf course to the main turf course. Law Abidin Citizen went on to win the San Simeon at 6 1/2 furlongs.
With the San Simeon the fourth of nine races scheduled, Santa Anita continued with its card as scheduled after the incident.
Kathy Guillermo, senior vice president of the People for the Ethical Treatment of Animals, released a statement in response to Arms runner's death: "Over the past two weeks, thoroughbred owners and trainers and the California Horse Racing Board have argued about medications, whipping, and the public perception of horse racing. But they did not take every measure needed to protect the horses. Both horses ran on the drug Lasix, which is known to cause dehydration and electrolyte loss. All drugs need to be banned entirely, and the known-safest racing surface — a synthetic track — must be used.
"Furthermore, PETA calls on Governor (Gavin) Newsom to urgently form an independent panel to investigate the training and veterinary practices in California racing, including the use of bisphosphonates and other medications that reportedly have been used indiscriminately. If the CHRB does not take every possible action to protect the horses, then racing should not be allowed to continue."