The veterinarian who injected 21 elite polo horses with a supplement before a championship match in Florida, also watched them die. He says the grief is "unbearable."
In his first interview since the death of horses, Argentine veterinarian Felix Crespo says he doesn't know if he'll ever be the same again.
A Florida pharmacy that mixed the supplement concoction has said the strength of one ingredient was incorrect.
Investigations into the horse deaths continue, but an exact cause has not been determined.
Necropsies of the bodies discovered bleeding in their lungs.