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 Wednesday, 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% 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 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.