A group of wild horse advocates have asked the U.S. District Court in Nevada to stop a planned Bureau of Land Management (BLM) mustang gather on grounds that the agency’s assessment of the animals’ environmental impact is flawed.

On July 7 the BLM is slated to begin gathering more than 1,700 animals collectively from the Triple B, Maverick-Medicine, and Antelope Valley Herd Management Areas (HMAs) in Nevada and the Cherry Springs Wild Horse Territory in Nevada. The ranges should have a combined herd population of between 472 and 889 animals, according to the agency.

Gathered mares released back to the range will receive the contraceptive porcine zona pellucida (PZP) prior to being returned to the HMAs or territory. Sex ratios of gathered animals returned to the HMAs could be adjusted to achieve an approximately 60% male to 40% female ratio.

In an agency press release BLM Spokesman Chris Hanefeld said the gather is necessary to reduce herd populations to appropriate management levels for each HMA