A wild horse advocacy group has filed a federal lawsuit aimed at stopping the Bureau of Land Management (BLM) from surgically sterilizing mares from an Oregon wild horse herd.

The Wild Free-Roaming Horse and Burro Act of 1971 protects wild horses and burros and places them under the BLM’s jurisdiction. The agency estimates that 67,000 wild horses currently reside on rangelands in 10 Western states.

In June, the BLM announced that in cooperation with Oregon State University it would “develop and evaluate safe and humane methods to spay” wild horse mares as a way to manage wild horse herd growth. The proposed surgeries would be performed on 100 mares residing in corrals in Hines, Oregon.

In response 35 wild horse advocacy groups went on record to oppose the research project claiming that the surgeries would be performed in a nonsterile environment and could result in complications including hemorrhage, infection, and colic that could be fatal