US District Court Judge Paul Friedman refused a request for a preliminary injunction to stop the Bureau of Land Management (BLM) beginning its muster in the so-called Calico Complex, an area of 500,000 acres comprising five formal herd management areas.
The bureau's plan is to remove about 80 per cent of the horses known to inhabit the rangeland in question. The muster is scheduled to begin on December 28.
Their plans were challenged in court by the group, In Defense of Animals, ecologist Craig Downer, and children's author Teri Farley, who were represented by attorney William Spriggs.
While Judge Friedman turned down the injunction, he saw merits in the advocate's legal argment around the ongoing placement of excess horses in long-term holding facilities in Oklahoma, Kansas and South Dakota.
Judge Friedman, in his 25-page decision, said the bureau's practice of holding tens of thousands of horses in long-term holding facilities in the Midwest, outside Nevada, did not appear to be authorised by law.
"The BLM's relocation of excess horses to those facilities for indefinite holding periods violates the plain language of Section 1339," the judge said.
"Furthermore, BLM's use of long-term holding facilities runs counter to the statute's mandate that the agency's management of wild horses occur at 'the minimal feasible level'.
"Long-term maintenance of thousands of horses in holding pens constitutes intensive management that was not contemplated by Congress when the Wild Horse Act was passed.
"... BLM's proposed confinement of hundreds or thousands of horses from the Calico Mountains Complex in long-term holding facilities in other states thus appears to contravene the unambiguous intent of Congress as expressed in statutory text and legislative history.
"It therefore is likely that the agency's interpretation of the statute as permitting such long-term holding and maintenance must be rejected ..."
The judge invited both parties to expedite briefing on that issue.
Based on that preliminary finding regarding long-term holding facilities, Judge Friedman said "the agency's [BLM] best option may be to postpone the [Calico] gather", but said that was for the bureau to decide while also noting potential harms in such a delay.
Horse advocates are now calling for a delay to the muster for the issues raised by the judge to be fully explored.
"The president should order a halt to this roundup until the legality of the long-term holding facilities is determined," said Spriggs.
"The BLM itself says this is not an emergency roundup, so there would be no harm in waiting for adjudication of this enormously important issue.
"We are on strong ground in charging that the BLM's policy of stockpiling tens of thousands of horses in the Midwest, off their rightful Western ranges, is contrary to law, the intent of Congress and the will of the American people," Spriggs concluded.
In Defense of Animals' president Elliot Katz urged the president to consider a delay, pointing to the 10,000-plus public submissions received by the bureau in assessing the merits of the muster.