Toxic Dose of Selenium Probably Killed Polo Ponies

April 28, 2009— -- An overdose of the mineral selenium probably caused the deaths of 21 polo horses at the U.S. Open Polo Championship, Florida's state veterinarian said today.

The horses, from Venezuela's Lechuza Caracas team, began collapsing last Sunday afternoon as they were unloaded from trailers at the International Polo Club Palm Beach, in Wellington, Fla., where they were scheduled to play in the U.S. Polo Open.

"Signs exhibited by the horses and their rapid deaths were consistent with toxic doses of selenium," Thomas Holt, the state veterinarian, said in a statement.

Holt did not say how the horses were given the mineral, but a Florida pharmacy has acknowledged that it had mixed an incorrect dosage of a chemical in a supplement given to the horses before their deaths.

The polo team, Lechuza Caracas, has said that the horses were injected with a vitamin compound that was similar to Biodyl, a supplement often used to treat fatigue in horses that is not approved for use in the United States.

Horses that were given the compound, which contained selenium, vitamin B, magnesium and potassium, died within three hours of being treated, the team said.

Selenium is a trace mineral that is "essential for normal cell function and health of animals," according to the Florida Department of Agriculture. It is often included in small quantities in supplements and feed for horses.

Large doses can be fatal, veterinarians said.

In a statement, U.S. Polo Association director Peter Rizzo said: "The Florida Department of Agriculture report confirms that what happened to the Lechuza Polo Team was a tragic accident."

He said the association was forming a committee to consider additional safety measures for horses.

The horses were reportedly showing no signs of illness Sunday morning, according to the Department of Agriculture.

By the time they were offloaded for the match, some of the animals were dead and the rest were showing signs of dizziness and having trouble breathing.