Nope we’ve not banned export for slaughter. More horses are being slaughtered for meat now, since the U.S. government quit funding inspectors in the U.S. in 2006.
Before they were slaughtered in U.S. facilities with a vet on site, humanely. Now they are doing it in Canada and Mexico, with little to no regulations, on the transfer and slaughter. That is the ones that aren’t being abandoned, starved, etc. In New Mexico alone, somewhere between 2,000- to 3,000 horses have been abandoned on public lands (BLM USFS, NPA and tribal lands).
The animals rights caused cruelty to horses to escalate after they convinced some in Congress to add riders to the ag appropriations bill, which were left off this time. The GAO issued a DAMNING report on the results in June 2011, that’s what led to this change.