FARGO — Theodore Roosevelt National Park rangers will resume a birth control program with the goal of eliminating the need for roundups to remove wild horses to keep the herd from overpopulating.

The park superintendent, Wendy Hart Ross, notified park horse “interest stakeholders” that about 20 mares will receive booster doses of a birth control drug the park has used experimentally to control the population of the herd.

The birth control drug will be administered to mares that received earlier vaccinations, but have returned to fertility, as well as 10 “randomly selected” mares that were part of the contraceptive research project.

“Vaccine will be administered remotely via syringe darts,” adding that reduced birth rates aren’t expected until 2021, Ross wrote in a letter dated Thursday, Sept. 12.

These three horses are members of one of the 19 bands of wild horses that roam Theodore Roosevelt National Park in western North Dakota. Forum file photo
These three horses are members of one of the 19 bands of wild horses that roam Theodore Roosevelt National Park in western North Dakota. Forum file photo

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After the removal of 14 young horses in early August, the population of the horse herd, which roams the park’s south unit, is about 135. Horses that are removed from the park are auctioned, and volunteers help to see that the horses find good homes.

The park expects to begin drafting a new management plan for the horse herd next year, Ross wrote in the notification letter. The current horse management plan was written in 1978.

Supporters of the park horses welcomed the announcement. They hope the birth control program, which has proven effective in testing at the park, will reduce or eliminate the need for future roundups, which are stressful for the horses, which form bands that function like extended families.

“We see this as a good thing,” said Mary Lou Weber, president of North Dakota Badlands Horse, a nonprofit group that helps Theodore Roosevelt National Park manage the park herd, including horse roundups.

“We kind of hate to see the herd get smaller and smaller, but we certainly see where the park is coming from,” she said.

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Chris Kman, who has a store in Medora that sells merchandise with photographs of the park horses and a Facebook group of the same name, “Chasing Horses,” also welcomed the announcement.

“I’m hoping that it means that they’re going to start giving birth control to the mares,” she said. “I just hope they give it to the right mares.”

By targeting mares that are old or are at risk for causing inbreeding problems, the park could help to maintain the health of the herd while controlling its population, she said.

In a study published last year, equine geneticists found that the genetic diversity of the horse herd was low and a matter of concern. The researchers did not find evidence of inbreeding, but said it was a potential problem and the genetic diversity of the herd should be increased.

Kman wrote an email to Ross after receiving notification listing mares she thought should be targeted for the birth control drug because they are old or in bands with family members, making inbreeding a risk.

Targeting high-risk mares should not be a problem for park staff, Kman said. “I don’t think it’s that difficult,” she said, adding that park staff have the necessary information.

Eileen Andes, chief of interpretation and public affairs for Theodore Roosevelt National Park, did not return emails and phone calls on Friday, Sept. 13, and Monday, Sept. 16, seeking comment.