A wild horse gather at the Stinkingwater Herd Management Area near Burns, Oregon. (Photo by Bureau of Land Management)

Federal officials want the public’s help in curbing Oregon’s growing wild horse population.

The Bureau of Land Management has asked for comment on three birth-control methods. The agency currently administers a birth-control vaccine that lasts up to two years but is looking for contraceptives that last longer.   

Oregon is currently home to about 4,500 wild horses. Sarah Bennett, a spokesperson for the agency’s Portland office, said Oregon can sustain about 2,700. 

Most wild horses in Oregon are in the southeast corner of the state near Nevada. Agency officials say they overgraze native plants, allowing invasive species to proliferate, and threaten other wildlife. They also affect water supplies. 

Not everyone agrees that Oregon has too many horses. Wild horse conservationists say the bureau needs to better manage land to provide ample habitat for the horses and to expand the use of the contraceptive it already uses, rather than investing in new ones. 

The public has until August 22 to comment. Afterwards, the agency will publish a decision on approving any of the project and, if approved, testing would begin in late 2022 and last up to five years. 

It’s proposing to test three contraceptives. 

The public can comment on the
birth-control proposals here.
The deadline for comments is Aug. 22. 

Two are vaccines and one is an intrauterine device, or IUD, which prevents the horse’s menstrual cycle.

“This would be the first study of IUDs in wild mares living on the range with fertile stallions,” Bennett said. 

One of the vaccines, GonaCon-Equine, causes an immune reaction that disrupts egg development and has proved to be safe in horses. It can last up to six years if the horse is boosted after the initial dose. The other vaccine, SpayVac, is similar to the current method of birth control the agency uses but is longer lasting. It has been tested before but had a lower efficacy rate. Higher quality versions of the vaccine are being made, and the agency would try injecting it in the neck and hind leg muscles to see if one is more effective. 

For the last few years, the bureau has administered a contraceptive called Porcine Zone Pellucida, extracted from the ovaries of pigs, which requires an annual booster after two years. It’s administered via darts that are shot at the horses from 30 to 50 yards away by volunteers and organizations that work with the agency.

In more remote areas, herds are gathered, treated and released. Bennet said wild horse populations can double in four years.

“The main issue is not a decreasing availability of land for the horses, but ever-increasing populations of wild horses on a constant amount of land,” she said. “This puts the wild horses at risk for thirst and starvation, especially during drought.”

Theresa Barbour, president of the nonprofit Oregon Wild Horse Organization disputes that. 

“We agree that the population needs to be controlled, however I don’t see an overpopulation,” Barbour said. “I see a reduction of the land available to them that makes it appear like a population issue.”

Barbour said land that used to be allocated to wild horse habitat has been shifted to livestock grazing and is about half the size of what it was 50 years ago.

The nonprofit advocacy group American Wild Horse Campaign said in a statement that the agency should invest more in its current birth control program. 

“The BLM has continually spent less than 1% of its budget on fertility control in wild herds. The agency must begin to invest more,” the statement said, adding that birth control was more humane than other population control methods, such as moving horses with helicopters to confine or relocate them. 

“Wild horses are present on just 12% of the land that the BLM manages. They are greatly outnumbered by commercial livestock whose damage to land health and contributions to climate change are well documented,” the group wrote.

Oregon Capital Chronicle

Oregon Capital Chronicle is part of States Newsroom, a network of news bureaus supported by grants and a coalition of donors as a 501c(3) public charity. Oregon Capital Chronicle maintains editorial independence. Contact Editor Lynne Terry for questions: info@oregoncapitalchronicle.com. Follow Oregon Capital Chronicle on Facebook and Twitter.

Alex Baumhardt has been a national radio producer focusing on education for American Public Media since 2017. She has reported from the Arctic to the Antarctic for national and international media, and from Minnesota and Oregon for The Washington Post. She previously worked in Iceland and Qatar and was a Fulbright scholar in Spain where she earned a master's degree in digital media. She's been a kayaking guide in Alaska, farmed on four continents and worked the night shift at several bakeries to support her reporting along the way.