An investigation into the deaths of dozens of horses at California's famed Santa Anita racetrack has found no evidence of criminal wrongdoing or animal cruelty, prosecutors in Los Angeles said Thursday.

"After a thorough investigation and review of the evidence, the district attorney's task force did not find evidence of criminal animal cruelty or unlawful conduct relating to the equine fatalities at Santa Anita Park," the Los Angeles County District Attorney's Office said in a 17-page report.

The report was issued following a probe involving multiple prosecutors and law enforcement officers following the deaths of 37 horses at Santa Anita over the past 12 months.

The investigation also said there was no evidence of injured horses being knowingly raced at Santa Anita or that the park had "pressured trainers and jockeys to race when there were concerns about weather or track conditions."

Los Angeles County District Attorney Jackie Lacey said in a statement that more could be done to ensure animal safety.

Lacey recommended that state regulators increase penalties for rules violations and establish a tip line to allow people to report suspected cases of animal cruelty or rules violations.

The prosecutor also called for mandated inspections of racing and training facilities as well as reviews of necropsy and veterinary records of horses that have died.

Los Angeles prosecutors found no evidence of criminal wrongdoing after investigating the deaths of dozens of horses at Santa Anita Park racetrack
Los Angeles prosecutors found no evidence of criminal wrongdoing after investigating the deaths of dozens of horses at Santa Anita Park racetrack GETTY IMAGES NORTH AMERICA / Sean M. Haffey

The report, which was issued one week before racing resumes at Santa Anita on December 26, also noted that horse fatalities at the track had fluctuated over the years.

The national average for racing fatalities in the United State was 1.68 deaths per 1,000 racing starts in 2018. Santa Anita's death rate over the same period was 2.04 per 1,000 starts.

The Stronach Group, which owns and operates Santa Anita, welcomed the prosecutors' findings.

"We are all committed to the same thing -- the highest level of equine safety and welfare -- and we will continue to do everything possible to promote equine and rider health and safety," the company said.

"We are gratified that the district attorney's report into the conduct and conditions at Santa Anita Park found no evidence of misconduct," it added.

However, the prosecutors' findings were criticised by animal rights activists who have long accused trainers of knowingly medicating injured horses in order to allow them to race.

"It's beyond credible that the district attorney doesn't see that trainers who medicate horses obviously know that they are injured and sore, so they should be criminally culpable if they then force them to race to their deaths," said Kathy Guillermo, senior vice president of People for the Ethical Treatment of Animals.