21 high goal polo ponies have died unexpectedly in Florida at the International Polo Club Palm Beach. Vets tried in vain to save the ponies before a US Open Championship match, but as they did so, others began to collapse.

The twenty one horses, with an estimated value of around two million US dollars all belonged to the Venezuelan-based Lechuza Caracas team.

Florida Agriculture and Consumer Services Commissioner Charles Bronson has launched an investigation into the deaths of the horses that collapsed after arriving in Wellington. Initially 14 horses died but by Sunday evening, an additional seven had perished overnight.

Mr Bronson said: "The initial review of the horse carcasses did not show any visible signs of trauma or disease that would indicate an obvious cause of death.”

"Our specialists will continue conducting more detailed testing until we get to the bottom of this tragedy."

State veterinary officials say the necropsies, which involve a visual inspection of the organs, only showed damage that was consistent with the clinical signs the horses were exhibiting before death. This included some lesions in the trachea and larynx which can be explained by the respiratory problems the horses were having prior to death.

State officials say evidence indicates this is not a contagious disease. They have returned to the polo facilities and stables, and say there are no additional cases of illness or deaths.

The Office of Agricultural Law Enforcement is working with Palm Beach County law enforcement to gather facts about the incident to determine the direction of the investigation.

The US Open is the oldest polo tournament in the United States. It is the culmination of the high-goal season at International Polo Club Palm Beach.

Team patrons, or player-sponsors, are known to bring out their best and most expensive strings of polo ponies for the prestigious tournament.