The sudden death of 21 polo horses at a championship event in Florida may have been caused by a toxin in the animals' feed, vitamins or supplements, say vets.
The horses from the Venezuelan-owned team Lechuza Caracas became ill just before a tournament match at the weekend.
The deaths have shocked the affluent equestrian and golfing community in central Palm Beach County, where the International Polo Club Palm Beach hosts the US Open Polo Championship every year.
Dr Scott Swerdlin, a veterinarian at Palm Beach Equine Clinic near the polo grounds, treated one of the sick horses and says it appeared the animals died of heart failure caused by some kind of toxin that could have been in tainted food, vitamins or supplements, or by some combination of all three that caused a toxic reaction.
Toxicology tests are being carried out.
The horses were worth around $3.5 million and will take 10 years to replace.