By SHANNON DININNY

Associated Press

SALT LAKE CITY (AP) -- The federal agency charged with managing wild horses and burros that roam freely across 11 Western states should consider sterilizing some mares to control booming mustang populations and protect rangelands, a citizen advisory panel recommended Tuesday.

The Bureau of Land Management has long struggled with how to manage growing horse herds on public lands, which can double naturally within five years if left unchecked. Horses have been injected with drugs and vaccines to slow reproduction and rounded up for adoption, but the agency currently has more horses in captivity than are left roaming the range, forcing the emphasis to shift to population control rather than roundups.

Nearly 60 percent of the agency's entire budget for the wild horse program is spent on housing horses.

Drugs currently used to slow reproduction in wild horse herds must be re-administered regularly because they only work for about a year, and drugs that work longer have not yet been approved for use on wild horses, said Dr. Boyd Spratling, a veterinarian from Deeth, Nev. and chairman of the bureau's Wild Horse and Burro Advisory Board.

Herd sizes can double naturally within five years if left unchecked.

Instead, spaying horses -- or surgically removing the ovaries of older mares -- eliminates the need for frequent roundups for adoption or to administer drugs, he said. Younger mares could still foal, allowing for genetic diversity in herds.

It's not a permanent solution, Spratling said, but a tool the BLM should have available for use in its effort to control herd sizes.

"Surgery is never 100 percent safe, but this is considered to be effective and relatively safe and has long been used in the racehorse industry," he said.

The BLM estimates there are 37,000 horses on public lands in the West. An additional 47,000 horses have been removed from the range and are being cared for in short-term or long-term holding areas.

Horse advocates have long argued that livestock should be removed from the range at a faster pace than horses, which they say have a legal right to be there under the Free-Roaming Wild Horse and Burro Act of 1971.

Ginger Kathrens, founder and executive director of Colorado-based horse advocacy group The Cloud Foundation, called the proposed surgical procedure too dangerous for use in the field.

"It's not been done successfully. It's a surgery in a field in a round pen in the dirt," she said. "How will it affect the health of the mare and the dynamic of the horse's family and the larger herd? They don't know."

However, board members raised concerns about the health of herds without intervention, pointing to a lack of feed on rangelands damaged by overgrazing and drought.

Those are the very conditions that have resulted in mass deaths of wildlife, such as deer, in the past, said Timothy Harvey of Campton, N.H., a board member and longtime horse trainer.

"I just don't want to see that kind of scenario develop," he said. "Anything we can do as a stopgap measure at this point, to head off the bus that's headed to the cliff, needs to be done."

In recent months, the BLM also has been criticized for allowing a horse slaughter proponent to buy hundreds of horses over the past five years for slaughter in Mexico. The agency acknowledged Monday that the Department of Interior's inspector general is investigating allegations that the Colorado man purchased more than 1,700 horses for slaughter in Mexico.

Current BLM policy requires those who purchase excess wild horses to sign papers promising they won't resell them for slaughter.

Copyright 2012 The Associated Press.