BILLINGS, Mont. (AP) — A federal judge in Montana temporarily stopped a mustang roundup planned for Sunday in response to a lawsuit filed by wildlife advocates who argued that it would destroy the genetic viability of a herd descended from the mounts of Spanish conquistadors.

U.S. District Judge Susan Watters on Friday ordered the Bureau of Land Management not to conduct the roundup on the 59-square mile (154-square kilometer) Pryor Mountain Wild House Range along the Montana-Wyoming border.

Watters also scheduled a Sept. 28 hearing on the advocates' broader request to stop the roundup.

The BLM planned to remove 17 of the roughly 150 horses on the range, by baiting the horses into corrals with food and water. They would later be put up for adoption.

Representatives for the agency on Saturday did not immediately return emails requesting comment on Watters' decision.

Officials have said the Pryor herd is too large for the arid, sparsely vegetated range and the horses have been overgrazing.

Colorado filmmaker Ginger Kathrens and the Cloud Foundation, an advocacy group, filed the lawsuit on Wednesday. They said removing the horses would eliminate animals with rare or unusual color patterns and affect the herd's unique genetic qualities.

In a statement, Kathrens said she hopes the hearing later this month will lead to a permanent hold on the roundup to "ensure a lasting future for this unique Spanish herd."

The Pryor range was created in 1968 as the second horse preserve in the nation. It was formed at a time when the capture and slaughter of wild horses for profit faced rising criticism, culminating three years later in the federal Wild and Free-Roaming Horse and Burro Act.

Across the U.S. wild horses and burros now far exceed U.S. government population goals, with 82,000 free-roaming horses and burros on almost 50,000-square miles of land in the West. About 46,000 wild horses and 1,600 burros are being held at government corrals and pastures, costing taxpayers $50 million annually.