The Associated Press reported today that the 21 polo ponies that died in Wellington, Fla., were killed by an overdose of selenium.

Florida‘s top veterinarian on Tuesday blamed the deaths of 21 elite polo horses on an overdose of a common mineral that helps muscles recover from fatigue.

Florida’s state veterinarian, Dr. Thomas J. Holt, said toxicology tests on the dead horses showed significantly increased selenium levels.

The horses from the Venezuelan-owned Lechuza Caracas team began collapsing April 19 as they were unloaded from trailers at the International Polo Club Palm Beach in Wellington before a championship match. Some died at the scene, others hours later.

“Signs exhibited by the horses and their rapid deaths were consistent with toxic doses of selenium,” Holt said.

Dr Holt said that the findings obtained at the department’s Animal Disease Diagnostic Laboratory in Kissimmee were confirmed by independent testing conducted at the University of Florida’s College of Veterinary Medicine in Gainesville, the University of California Davis Animal Health and Food Safety laboratory, and at testing facilities at Cornell University in Ithaca, New York.