PORTLAND, Ore. — The U.S. Bureau of Land Management has dropped a research effort that would have led to the surgical sterilization of more than 200 wild mares at a facility in Oregon.

The agency said Friday the decision was made in response to litigation from groups that assert the procedures to be researched were unnecessary and barbaric.

Advocates for wild horses sought to halt the study or, at the very least, allow the media and the public to observe and record it.

“This decision, though not made lightly, is in response to litigation that could have put the wild horses, BLM staff and our research partners at risk by requiring unnecessary persons or equipment be placed within the small confines of the space where the procedures would take place,” the BLM said in a statement released through its Portland office.

BLM spokesman Greg Shine said the agency had no comment beyond the statement.

The BLM wanted to study three methods to determine whether they are safe, effective options for controlling the wild horse population.

Of the three methods, the advocates were most concerned about a procedure that involves removing ovaries from sedated, pregnant mares in various gestational stages. The veterinarian reaches into the mare’s abdomen through the vagina to sever and remove the ovaries.

The Cloud Foundation and American Wild Horse Preservation Campaign filed a lawsuit last month seeking the presence of outside observers. Two other groups, Front Range Equine Rescue and Friends of Animals, sued to stop the research that would have been done at the Wild Horse Corral Facility in Hines, Oregon.