U.S. District Judge Kent Dawson found that America's Wild Horse Advocates had no scientific backing to their objections to the roundup, the Las Vegas Review-Journal reported. Dawson scheduled a hearing for Jan. 30.

The Bureau of Land Management plans to begin corralling burros and horses on Tuesday. Healthy animals under the age of 5 will be put up for adoption, while older ones may go to sanctuaries.

The BLM hopes to reduce the herd in the area by 95 percent, rounding up 266 horses and 799 burros.

"I'm extremely disappointed; I have this pit in the bottom of my stomach," Billie Young of the advocacy group said. "Even though we have a hearing date at the end of January, all the horses will already be gone."

Kirsten Cannon, a spokeswoman for the BLM, said that overgrazing by horses and burros threatens plants in the region and other species that depend on those plants. The large size of the herd means that the horses and burros have also become unhealthy.