RENO, Nev. (AP) — It will take $5 billion and 15 years to get an overpopulation of wild horses under control on federal lands across the West, the acting head of the U.S. Bureau of Land Management said recently, adding that several developments have made him more optimistic about his agency's ability to get the job done.

William Perry Pendley said the agency adopted out more than 7,000 mustangs and burros captured last year — the most in 15 years and a 54 percent increase from the previous year.

He said that helps clear space in government holding pens, so they can accelerate roundups while scientists develop new fertility-control drugs to eventually shrink the size of the herds from 88,000 to the 27,000 he says the range can sustain. He said a new coalition of animal welfare advocates and ranchers is helping promote solutions and Congress appears willing to help.

Pendley, who is awaiting Senate confirmation as director, said the agency is in the process of hiring additional staff to speed roundups in Nevada, the state with the most horses.

“I'm not going to speculate on what Congress is going to do about money,” Pendley said. “But I know there is a sense of sincerity on the Hill about this issue. They get it.”

The Senate Appropriations Committee approved $35 million last month for a new package of mustang proposals supported by an unprecedented alliance including the Humane Society of the United States, American Society for the Prevention of Cruelty to Animals, National Cattlemen's Beef Association and American Farm Bureau Federation.

They say it would eliminate the threat of slaughter for thousands of free-roaming horses and shrink the size of herds primarily through expanded fertility controls on the range and increased roundups in certain areas.

The proposal has been condemned by the largest and oldest mustang protection groups in the West, including the American Wild Horse Campaign and Friends of Animals.

“This proposal, which is really a betrayal by so-called wild horse advocates who are in bed with the meat industry, is management for extinction and putting money toward it is a step toward eradicating these iconic animals from our public lands,” Friends of Animals President Priscilla Feral said.

In July, then-Acting BLM Director Casey Hammond said the Trump administration won't pursue lethal measures such as euthanasia or selling horses for slaughter.

But critics say the new plan could allow for sterilization of mares. They argue the animals must be permitted to roam the range in federally protected management areas established under the Free-Roaming Horse and Burro Act of 1971. They say BLM's population quotas are often outdated and lack scientific data to support roundups to cull herd sizes.

The $35 million the Senate committee approved is part of the $35.8 billion Interior Department appropriation bill. It's not clear when the full Senate will consider the measure.

Pendley said the agency is spending $50 million a year to house 50,000 captured horses in government corals and another $30 million in associated costs.

Doug Busselman, executive director of the Nevada Farm Bureau, said his group still wants Congress to allow the government to sell excess horses without the current ban on their resale for slaughter.

“As long as the numbers are so far above appropriate management levels, the tools of fertility control and adoption don't accomplish the needs for having wild horse and burro populations match the carrying capacity of the herd management levels and the destruction of the habitat will continue,” he said in a statement.

Conservationists say more damage is caused by the cattle and sheep that graze on public lands at a ratio of 15-to-1 mustangs.