WELLINGTON, Fla. The sudden death of 21 polo horses in Florida might have been caused by a toxin that has yet to be identified by tests and could have been in the animals' feed, vitamins or supplements, veterinarians said today.

The horses from the Venezuelan-owned team Lechuza Caracas sickened just before a tournament Sunday, collapsing and dying on the scene or while being treated at vet clinics or transported, officials said.

Dr. Scott Swerdlin, a veterinarian at Palm Beach Equine Clinic near the polo grounds, treated one of the sick horses. He said it appeared the animals died of heart failure caused by some kind of toxin that could have been in tainted food, vitamins or supplements or some combination of all three that caused a toxic reaction.

"A combination of something with an error in something that was given to these horses caused this toxic reaction," Swerdlin told reporters.

It could take days or weeks to get the results of toxicology tests that could identify the toxin, he said.

Another veterinarian who was at the scene said something triggered heart failure among the horses.

"Well clearly, it's an intoxication, clearly there's some sort of a poison," Dr. James Belden told NBC's "Today Show."

The team is owned by Venezuelan businessman Victor Vargas, but most of the horses and players are Argentine, Swerdlin said. The team travels most of the year.

Swerdlin said the team has up to 60 horses. All of those who fell sick have died, he said.

By The Associated Press