The 21 polo ponies that died in Florida were given incorrectly mixed medication, H&C can reveal.

A Florida pharmacy said it had mixed the medication given to the ponies that died, as investigators awaited the result of toxicology tests that could shed further light on the cause of death.

Franck's Pharmacy of Ocala, Florida, said it had prepared a medication used to treat the 21 horses on the order of a vet.

The horses, which belonged to the Venezuelan polo team Lechuza Caracas, collapsed and suffered from respiratory failure at the U.S. Open Polo Championships in Florida.

Local police and the State's Department of Agriculture have launched an investigation to determine if a crime has been committed.

Following the tragedy, Franck's chief operations officer Jennifer Beckett, said: "The strength of an ingredient in the medication was incorrect."

"We extend our most sincere condolences to the horses' owners, the Lechuza Polo team and the members of the United States Polo Association," the statement said. "We share their grief and sadness."

Lechuza's team captain, Juan Martin Nero, told an Argentine newspaper that a vitamin supplement given to the horses probably caused their deaths.

It appears that the ponies who died were given a mixture of vitamin B, potassium, magnesium and selenium, prepared in Florida by a compounding pharmacy.

Terence McElroy, a spokesman for the Department of Agriculture, said initial round of toxicology tests should be known in the next few days, but further tests may be required to get to the bottom of the ponies’ cause of death.

A memorial ceremony for the horses was held on Thursday during a match at the International Polo Club Palm Beach.