The society is offering $US5000 for information leading to the identification, arrest and conviction of the person or persons responsible for slaughtering at least 17 horses in the Miami-Dade County area since January.
It said was doubling its standard $US2500 reward for information offered in February since the killings appear ongoing.
Since January, at least 17 horses have been found slaughtered in their pastures or barns, or found dead and abandoned at the side of roads.
The horses appear to have been butchered for their meat.
In the latest case, an appaloosa mare named Linda was found killed in her stable with her two-month-old foal nearby.
"These horses were beloved companions found barbarically killed for their meat," said Laura Bevan, the society's eastern regional director based in Tallahassee.
"The horses must have suffered horribly, and now their owners grieve their needless deaths."