The illicit trade is believed to be behind the spate of horse killings in Miami-Dade and neighbouring Broward County this year.
At least 20 horses have been butchered and their remains often dumped on roadsides, angering horse owners and sparking demands for action.
Authorities believe horse meat can fetch up to $U20 a pound on the black market. While some arrests have been made in relation to the police investigation, authorities are not convinced they have got to the heart of the problem.
NBC Miami and the Miami Herald report that a multi-agency operation this week, involving police, county officials, Florida health inspectors and federal food safety officers, targeted an area known as the C-9 Basin.
The area in the county's rural western reaches and has long been the home to illegal slaughterhouses. Such operations are suspected of being behind the illegal trade in horse meat.
Reports suggest that while no stores of illegal horse meat were located, multiple violations of business, health and environmental regulations were found and at least one unlicensed slaughterhouse was found and is being shut down.
County authorities shut down six illegal slaughterhouses from 2001 to 2005 in the area.