U.S. District Judge Miranda Du's formal order lifted an injunction she issued last week blocking the roundup of 50 horses near the Idaho-Nevada line.
"The judge has begun what the BLM has failed to do, and that is to establish humane standards for roundups," said Deniz Bolbol, spokeswoman for the American Wild Horse Preservation Campaign.
The judge prohibited the routine use of "hot shot/electric prod treatments" to expedite movement of horses through gathering and loading chutes, allowing their use only "as necessary to ensure the safety and security of the horses."
Also, BLM contract helicopter pilots who chase the horses toward the gathering traps must make sure that slower young foals aren't separated from the herd. And the judge specifically forbade the agency from driving horses into barbed-wire fences, as they did with several earlier in the roundup at the Owyhee complex about 90 miles northwest of Elko.
Laura Leigh, a photographer and director of Wild Horse Education who has been battling BLM over a series of roundups for years, captured that incident on video.
It was among the evidence she submitted in obtaining last week's emergency injunction, along with footage of wranglers repeatedly shocking horses in a loading chute on Nov. 30.
She hailed the ruling as a significant victory.
"Three years of running this grueling marathon from range to courtroom to gain an honest conversation about the inhumane handling of an American treasure and we now have the very first specific language toward actually gaining the first humane care standard," Leigh said in an email to The Associated Press late Thursday.
During a hearing in her Las Vegas courtroom earlier Thursday, Du said she intended to grant the government's request to lift the injunction because opponents had failed to prove the agency lacked authority to remove the mustangs from the high desert.
But she also indicated she was inclined to include language in the order addressing concerns about the allegations of abuse, including repeated shocking of mustangs and running animals to the point of exhaustion.
"If I were to allow the gather to continue, I would want to ensure the horses were gathered in a humane way, as the BLM is required to do by statute," she told Justice Department lawyer Erik Petersen, referring to the Wild Free-Roaming Horse and Burros Act of 1971.
BLM argues the herd in the Owyhee Horse Management Area is too large to be sustained given lingering drought. The agency has warned that some of the animals could die if they aren't removed before spring.
Wild horse protection advocates countered by accusing the agency of shamefully exaggerating the threat to the animals in an area.
"I think it is fiction, your honor," said Gordon Cowan, a Reno lawyer for Leigh. "There's really no emergency out there. There's no proof of stress on the range."