It was clear the animal had been butchered for meat, which finds ready buyers on the local black market, where it can fetch up to $US40 a pound.
Police are investigating.
It is the third discovery of a slaughtered horse in the county in two months, and was in the same spot where a butchered horse was found a month ago.
Richard Couto, who founded the Animal Recovery Mission and is a vocal campaigner against the illegal trade, told CBS4: "The animal was tortured and is in roughly 20 to 30 pieces behind me.
"There are some sick people out there that have been doing this in Miami-Dade County for 50 years. These are violent, evil people. These are nasty, nasty people."
Couto said it was likely the horse was slaughtered elsewhere and its remains dumped in the spot.