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Sound Science Helps Manage America's Wild Horses

The Humane Society of the United States

by Julie Hauserman

On private horse sanctuaries in South Dakota, Dave Pauli and Heidi Hopkins are working on a humane solution to manage America’s magnificent wild horses.

Pauli, director of The Humane Society of the United States’ Western Region, and Hopkins, HSUS Wyoming state director and wild horse program manager, have been on the ground this spring, administering birth control doses to wild mares.

Humane Solution

The work is particularly important in light of what’s happening in Congress, where The HSUS is working to overturn a provision that allows the government to round up wild horses and send them to slaughter.

Anyone who handles unwanted pets knows that the first logical step to control population is to spay and neuter animals. A nationwide wild horse adoption program has helped save many of America’s beloved wild horses, but additional tools are needed to help protect the herds.

Hopkins believes the adoption program, combined with a contraceptive program, could prove to be a humane solution. On the South Dakota sanctuaries, a team uses a contraceptive vaccine on controlled populations of wild mares and closely documents the results.

“This is part of the solution for wild horses,” Pauli said. “This is a non-lethal tool that can minimize the need to round up horses and put them through all that stress.

“It is good science” he continued, “and it is a reversible tool for birth control that can prevent excess births of horses without changing the behavior of the herd.”

Good Science

In March, April, and early May, Pauli and Hopkins headed out with Jay F. Kirkpatrick, director of the nonprofit Science and Conservation Center at ZooMontana in Billings, to track down wild horses at the South Dakota ranches and inject them with PZP, the immuno-contraceptive drug that Kirkpatrick developed and has been using for 20 years on a variety of animals.

The drug triggers a mare’s immune system to reject fertilization and has been used in a series of research projects in zoos, and on public and private lands. The HSUS holds an Investigational New Drug Permit from the Food & Drug Administration to conduct research using the contraceptive vaccine. Studies are underway on populations of deer, elephants, bears, and other species.

The wild horses vaccinated this spring were rescued from U.S. Bureau of Land Management lands and are now protected at the Black Hills Wild Horse Sanctuary in Hot Springs, S.D., and at the International Society for the Protection of Mustangs and Burros in Lantry, S.D.

“We treated 140 of them this spring,” said Pauli. “These mares, in theory, will have 140 fewer foals next year.”

Controlling herd reproduction with PZP, Hopkins says, is obviously a preferred alternative to killing innocent animals. Before joining The HSUS, Hopkins worked for the BLM, where she took a lead role in helping control Nevada’s wild horse and burro population. 

Saving America's Wild Horses

For more than 30 years, wild horses and burros were protected from slaughter under the Wild and Free-Roaming Horses and Burros Act of 1971. But a 2004 midnight amendment by former Sen. Conrad Burns, R-Montana, gutted these longstanding protections. In minutes, with no public review, wild horses were robbed of protection from commercial sale and slaughter.

The HSUS is now working hard to help pass H.R. 1018—Restoring Our American Mustangs Act, introduced by Reps. Nick Rahall (D-WV) and Raúl Grijalva (D-AZ)—which would prevent the wholesale killing of healthy wild horses and promote on-the-range management like immunocontraception.

In the field in South Dakota, Pauli, Hopkins, Kirkpatrick, and others have been heading out on the ranches, looking for wild horses. First, they use hay or water to attract the herds.

They try to stay hidden and use compressed-air guns to shoot small contraceptive-filled darts at the horses. The darts sting a little, like an insect bite. The darts have an antibiotic cream on them, and they fall off after the syringe automatically injects the contraceptive. Pauli, Hopkins and the others in the team then walk the land with metal detectors to collect the used darts.

During the first year, the mares need a booster shot, so the team heads out again a month later. The team keeps painstaking track of which horses received PZP by making detailed notes of each mare’s coloring and unusual characteristics in a three-ring binder. Each mare gets her own page, along with a digital picture.

“This work in South Dakota is really important because we want to emphasize to the Bureau of Land Management that this drug is effective and useful,” Hopkins said. “When they see this drug used successfully in these sanctuaries, the agency will have even more evidence of its effectiveness and an excellent example of how to use it in the wild herds on federal lands.”

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