By Scott Sonner, AP

RENO — The federal government has abandoned plans — at least for now — to round up more than 300 wild horses in Northern Nevada after a U.S. judge temporarily blocked the effort last month for fear of harm to the mustangs.

The agency won’t move forward with the roundup in the Pine Nut Range southeast of Carson City until it completes another review of potential environmental effects, lawyers for the U.S. Bureau of Land Management said in papers filed in federal court in Reno.

Judge Larry Hicks had granted a restraining order sought by horse advocates preventing the roundup until he could hear further arguments from both sides on the merits of the case.

Opponents say the Bureau of Land Management was relying on a nearly 5-year-old environmental analysis that ignores the latest scientific evidence about the dangers posed by injecting female horses with a fertility drug that keeps them from reproducing for two years.

Lawyers for Friends of Animals and Protect Mustangs said there’s been significant new research about the potential harms of PZP since the federal agency reviewed the effects in 2010. New studies confirm earlier concerns that the interference with the wild herds prompts mares unable to become pregnant to leave in search of stallions in other bands of mustangs, they said.

Hicks said in his Feb. 11 ruling that the agency appeared to have violated federal law, including the National Environmental Policy Act requiring a more stringent examination of the effects than the one Bureau of Land Management scientists conducted.

Leon Thomas, the federal agency’s field manager for the Sierra Front based in Carson City, said in an affidavit filed in the government’s voluntary dismissal of the case late Tuesday that the agency won’t implement the record of decision it issued last year to permanently remove 200 horses and return about 130 back to the range, about half of those mares that would have been injected with PZP.

The Bureau of Land Management will prepare a new document “analyzing the environmental impacts associated with gathering, treating and removing excess wild horses form the Pine Nut (management area), and a new decision will be issued before implementing any such gather,” he said.

Agency spokeswoman Lisa Ross said Wednesday that the soonest the new review could be completed and clear requirements for public comment would be sometime in the fall, “depending on available funding and holding space.”

Horse advocates said the move marked an important victory in their ongoing battle with the federal agency and ranchers over forage on public rangeland — much of it in the throes of drought — in 10 states stretching from Montana to Arizona.

“This case highlights some of the deficiencies with BLM’s current management of wild horses, and I hope that in the future BLM considers its obligations to involve the public on decisions that affect our public lands,” said Jennifer Barnes, staff attorney for Friends of Animals.

The Bureau of Land Management maintains there are nearly twice as many horse in the Pine Nut Range as the high desert habitat can support without causing ecological damage, some of which could hurt the imperiled sage grouse.

Ross said the agency has no intention of discontinuing use of PZP to help to suppress growth of the herds that naturally double about every five years if left unchecked.

“The BLM did not appeal the February 11 injunction due to the concern for the welfare of the horses,” she said in an email to the Associated Press. “The time required to file an appeal would have resulted in a gather during foaling season, which generally starts March 1. Gathering during foaling season presents an increased risk to new foals and pregnant mares. ”