A group of U.S. senators has asked Secretary of the Interior David Bernhardt to scrap a Bureau of Land Management (BLM) plan to surgically sterilize mustang mares to control herd growth at the Warm Springs Horse Management Area (HMA) in Oregon.

Located on 474,547 acres 20 miles southwest of Burns, Oregon, the BLM’s estimated appropriate management level (AML) for the Warm Springs HMA is between 96 and 178 wild horses. Currently an estimated 738 mustangs reside there. The BLM would perform the procedure on about 100 of the Warm Springs HMA mares.

The controversial spay plan (the procedure is known as ovariectomy via colpotomy) involves the manual insertion of a metal rod to locate and remove a mare’s ovaries. Critics of the procedure maintain that it can cause excessive bleeding and even death. The latest plan is the agency’s most recent attempt to use the surgical procedure to permanently sterilize mares to control herd growth. In 2018 the plan was put on hold when a federal judge issued a temporary order to halt it.

In their July 17 letter Senators Corey Booker (D-NJ), Tom Udall (D-New Mexico), Kamala Harris (D-California), Ed Markey (D-Massachusetts), Richard Blumenthal (D-Connecticut), Robert Menendez (D-New Jersey), Christopher Coons (D-Delaware), and Dianne Feinstein (D-California) asked Bernhardt to abandon the spay plan on grounds that it threatens the mustangs’ welfare and is contrary to public opinion.

“We urge the BLM to drop this controversial plan and instead actively peruse humane and scientifically supported fertility control projects such as the porcine zona pellucida (fertility) vaccine (PZP) that enjoy broad support and pose significantly less risk of harm to the federally protected wild horses,” the letter said. “At a minimum, independent veterinary and welfare oversight is necessary if this project is to move forward.”

No one from the BLM was available to comment on the letter.

Joanna Grossman, PhD, equine program manager for the Animal Welfare Institute (AWI) praised the senators for asking the BLM to nix the plan.

“We appreciate their leadership in urging the BLM to put a permanent end to this misguided research proposal and focus instead on implementing effective and humane fertility control options to manage our nation’s wild horses,” Grossman said.

But not all oppose the spay plan. Some veterinarians have frequently surgically spayed mares for medical and behavioral reasons, said Tom Lenz, DVM, MS, Dipl. ACT, who serves on the BLM Wild Horse and Burro Advisory Committee but spoke to The Horse on his own behalf.

He believes herd population control is so critical to the welfare of wild herds that the BLM must use every tool available to achieve it.

“Spaying should be part of a number of solutions to herd population control,” Lenz said.

The plan is slated to be implemented later this year.