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BLM works on new fertility control vaccine for wild horses

by Wyoming Livestock Roundup

In a newsletter update published July 9, the Bureau of Land Management (BLM) explains it is currently working on testing a promising new fertility control vaccine, which could help address the growing overpopulation of wild horses on public rangelands.

            In March 2019, BLM conducted an environmental analysis and a final decision record was issued. 

According to BLM, testing of the vaccine began May 12 and is currently underway in Carson City, Nev., in collaboration with the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service’s National Wildlife Research Center.

            “For decades the BLM has sought a long-term vaccine that could help effectively and humanely control the rapid growth of wild horse and burro populations on public lands,” says BLM Deputy Director for Policy and Programs William Perry Pendley.

He continues, “Now, more than ever, an all-of-the-above approach is needed, as a rapidly growing overpopulation of wild horses and burros threatens the long-term health of our public lands. With the start of this trial, BLM has taken a big and important step forward to developing better, more effective population management tools that can help solve the growing crisis.” 

Vaccine study

            The BLM notes their project follows in the footsteps of a previous study, which safely and effectively tested a multi-dose version of an oocyte growth factor (OGF) vaccine in domestic horses. However, the BLM is working toward an effective one-dose version. 

As part of their study, 16 wild mares, which were previously gathered, were treated with the fertility control vaccine. Once the vaccine takes effect, the mares will be placed in a pen with a stallion, and researchers will monitor the mares’ response to the vaccine, compared to a control group. 

While big steps in the process have been taken, BLM points out the study is still in its early infancy. 

“If proven viable, the OGF vaccine could help bolster existing methods used to manage wild horse populations,” BLM states. “The most common fertility control vaccines for wild horses in use today are short lasting and require near annual retreatment to remain effective. A single-dose vaccine that can last multiple years, such as the OGF vaccine, would provide a number of benefits including requiring fewer instances of gathering animals for displacement or permanent removal.”

Population estimates

The new fertility control trial comes as BLM releases annual wild horse and burro population estimates, showing widespread overpopulation in herds across the West. 

According to BLM estimates, as of March 1, Nevada had the highest population of wild horses and burros at 51,528 head total, with 46,974 horses and 4,554 burros.

The second highest total of 12,241 wild horses and burros is estimated in California, with 8,702 wild horses and 3,539 burros.

Wyoming rounded out the top three highest population states with 8,706 head of wild horses.

“The estimated population of approximately 95,000 wild horses and burros is the most ever estimated by BLM and compares to approximately 27,000 that roamed the land when the animals became federally protected and managed under the 1971 Wild Free-Roaming Horses and Burros Act,” BLM notes.

“Without intervention by management officials, wild horse and burro herds on public lands increase rapidly, doubling in just four to five years,” the agency explains. “Many herds rely on arid environments with little water or forage. Constant overpopulation can stress critical ecosystems to the brink, causing severe damage to riparian and rangeland resources. Moreover, overpopulation leads to the inhumane death of the horses and burros from thirst or starvation.”

Other management strategies 

In addition to supporting the development of better fertility control tools, the BLM has taken action to manage overpopulation and protect land health. 

For example, since 2008, the agency has gathered more wild horses and burros from overpopulated herds than the previous five years combined.

 In addition, the BLM has also taken steps to reduce the number of unadopted and unsold animals in its off-range holding facilities. 

In fact, due in part to their cash-incentive program, the BLM recently announced adoptions and sales of wild horses and burros through the Wild Horse and Burro Program reached a 15-year high. The agency notes they adopted out more than 6,000 animals in the past year, saving taxpayers $170 million.

            “We’re excited the public has responded so strongly to this innovative program,” said Casey Hammond, principal deputy assistant secretary for land and minerals management. “The successful use of incentives to increase adoption rates is a win for all involved, saving taxpayers hundreds of millions of dollars, reducing the overpopulation of wild horses and burros on the range and helping these animals find homes with families who will care for and enjoy them for years to come.” 

            As of July 22, the BLM will be restarting their adoption program by appointment only. Those interested can contact the Mantle Adoption and Training Facility at 307-775-6762 or the Rock Springs Corrals at 307-352-0292.

            Hannah Bugas is the managing editor for the Wyoming Livestock Roundup. Send comments on this article to

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