MIAMI (Reuters) – Florida launched an investigation on Monday into the deaths of 21 polo ponies from a Venezuelan team competing at the U.S. Open Polo Championship.

The horses collapsed after appearing dizzy and disoriented as the Lechuza Caracas team prepared for an afternoon match on Sunday at the International Polo Club of Palm Beach in Wellington, Florida, officials said.

“Because of the very rapid onset of sickness and death, state officials suspect these deaths were a result of an adverse drug reaction or toxicity,” Florida’s Department of Agriculture said in a statement announcing its investigation.

“At this time there is no evidence that these horses were affected with an infectious or contagious disease,” it said.

The horses were kept at the Lechuza Caracas equestrian facility near the polo grounds in Wellington, about 70 miles north of Miami, and did not show any signs of illness on Sunday morning, officials said.

But when they were offloaded from trailers at the polo club, some had died and the others were “showing severe symptoms of depression, respiratory problems, incoordination and recumbency,” the agriculture department said.

“It could be the water, hay, bedding, we just don’t know,” John Wash, president of club operations, told local media.

The Lechuza Caracas team is owned by millionaire Venezuelan banker Victor Vargas, who has been playing polo since he was 24, according to the North American Polo League’s website. Vargas was re-elected president of the Venezuelan Banking Association in April.

His team withdrew from the championship following the deaths, the league said.

Lechuza Caracas team veterinarian James Belden said the horses died one by one, “almost certainly of an intoxication of some sort that they consumed,” the Palm Beach Post reported.

Belden said it was unlikely that the horses had died from tainted medication or had been given anabolic steroids because they are banned in England, where the team competes.

“I’ve been in practice 50 years. I’ve never seen anything like this,” he told the newspaper.

Necropsies and toxicology tests were being performed on the horses, but it could take several days to learn the results.

“This is a tragic situation and we are working hard to determine what happened,” Agriculture Commissioner Charles Bronson said. “But it would be irresponsible to speculate on what may have killed the horses. We will wait until the facts are in before making any specific comments on the case.”

(Reporting by Jim Loney; Editing by Jane Sutton and Eric Walsh)