RENO, Nev. (AP) — Sen. Dianne Feinstein is calling on federal land managers to conduct an investigation to determine how many of the wild horses captured on public lands in the West end up at slaughterhouses.

The California Democrat is urging the U.S. Bureau of Land Management to reevaluate the $1,000 cash payments it offers those who adopt the mustangs.

Horse advocates say the money provides an unintended incentive to obtain the mustangs then illegally resell them for slaughter.

The agency announced last month it's tightening protections to guard against illegal resales. But critics say they've documented resales for slaughter for decades.

They say the problem will continue until the cash payments end.