Polo officials in the United States have launched an investigation after 21 horses died in mysterious circumstances as they were due to compete in a match in Florida on Sunday.

Fifteen of the horses, who belonged to the Venezuelan-based Lechuza Caracas died ahead of the match as they were being kept in team trailers at the International Polo Club Palm Beach. Six more horses which had been kept in the same trailer died later, according to a report on CNN.com.

A spokesman for Lechuza Caracas, who play in the North American Polo League, told the Sun-Sentinel newspaper that all of the horses had been aged between 10 and 11 years old and were worth at least $100,000 each. Polo teams typically take 50 to 60 horses to a match, rotating them throughout the game.

“Everybody is kind of in shock and trying to figure out what happened,” he said. “Nobody can recall an incident in which this many horses have died at once.”

Celeste Kunz, chief examining veterinarian at the New York Racing Association , said Monday that she suspected a tainted substance was injected into the horses.

“[It was] something that was administered for it to work in a short amount of time and have an animal succumb that quickly,” Kunz told CNN. “My thought is that something was injected because it would have to affect the central nervous system.”

Kunz said anabolic steroids were unlikely to have caused the deaths because the drugs take longer to take effect.
“It takes at least five days for [anabolic steroids] to really work, and the effects aren’t real obvious at first,” she said. “Most of the time [anabolic steroids] are used to build up their muscularity.”

Peter Rizzo, executive director of the United States Polo Association, who was at the match and saw the horses drop to the ground, described the incident and surreal and unprecedented.

“It is a horrible tragedy,” he told CNN.

A spokesman for the Florida Department of Agriculture and Consumer Services said that the bodies of the horses would be tested to determine whether there was a common denominator in the deaths.