Twenty-one polo ponies have died from a mystery illness in Florida.

At least 14 ponies from the Venezuelan polo team Lechuza Caracas died yesterday (Sunday 19 April) — and the death toll rose to 21 overnight.

The ponies were due to take part in the US Open Polo Championships at International Polo Club Palm Beach when they were struck down.

Two of the ponies collapsed when being unloaded from a trailer and others were reported to be showing signs of dizziness and disorientation.

The ponies were hooked up to intravenous drips and cooled with fans and water.

“They started getting dizzy,” polo club spokesman Tim O’Connor told a local newspaper. “They dropped down right onto the grass.”

Screens were put up to hide the ponies from the crowd’s view as seven died at the club. The others died after being taken elsewhere.

The bodies have been taken to a state agricultural laboratory for tests.

Vets at the Palm Beach Equine Clinic currently think the ponies had been exposed to a toxin — though they are unclear whether it was airborn or ingested.

“It could be the water, hay, bedding. We just don’t know. When we find out what it is, we will take all the necessary actions,” John A. Wash, the polo club’s president of club operations, told the newspaper.

Each of the ponies were all between 10 and 11 years old and worth about $100,000.

The match was postponed and an exhibition game was played instead.

More to follow