CNN) -- Florida agriculture scientists are performing necropsies Monday on 21 horses that died as they were prepared to compete in a Sunday polo match in Wellington, Florida.
"We'll be testing blood and tissue to see what the common denominator was here -- was it something injected, was it bad water and so forth," said Terence McElroy, a spokesman for the Florida Department of Agriculture and Consumer Services.
The horses were part of the Venezuelan-based Lechuza Caracas team and were being kept at the team's trailers on the grounds of the International Polo Club Palm Beach. Fifteen horses that seemed disoriented died before Sunday's match, said McElroy, and their bodies were sent to the state-run Kissimmee Diagnostic Laboratories near Orlando, Florida.
Two horses initially collapsed, and as veterinarians and team officials scrambled to revive them, five others became dizzy, Tim O'Connor, spokesman for
the polo club, said Sunday. 
Watch as vets search for clues
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Were these murders or accidental deaths? How much do we know about the Lechuza Caracas? Do they have any enemies in this country?
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Some of those horses died immediately, but some lingered for about 45 minutes, Dr. Scott Swerdlin of the Palm Beach Equine Clinic said, according to a report in the Sun-Sentinel newspaper. The clinic is the International Polo Club's consulting veterinarian group, the newspaper said.
Six of the 21 horses were kept overnight in the same trailer in Wellington, said McElroy, and died overnight there. Their bodies have not been taken to the Kissimmee lab.
The U.S. Polo Association, the sport's governing body, is expected to open an investigation Monday.
Celeste Kunz, chief examining veterinarian at the New York Racing Association and a 19-year veterinarian, 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 said. "My thought is that something was injected because it would have to affect the central nervous system."
She dismissed the chances that the horses ingested something because it would take longer to metabolize and they would show signs of illness sooner than they did before the match.
Anabolic steroids are not likely to have caused the deaths either, she said.
"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."
Each team brings between 40 to 60 horses for matches. The ponies are continuously switched out throughout a match to keep them from overexerting themselves, O'Connor said.
The horses were between 10 and 11 years old and were valued at about $100,000 each, club spokesman O'Connor said, according to the Sun-Sentinel.
A meeting will be held to determine whether Lechuza Caracas will compete at a later date, he said.
"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.
From just the clues above, YOU may be able to solve this mystery. For the answer, please turn to page 87 at the back of this book.
