Date:  June 5, 2013





New Report Offers Science-Based Strategies for Management of Western Free-Ranging Horses and Burros; ‘Business-as-Usual’ Practices Will Be Increasingly Expensive and Unproductive for BLM


WASHINGTON -- The U.S. Bureau of Land Management’s (BLM) current practice of removing free-ranging horses from public lands promotes a high population growth rate, and maintaining them in long-term holding facilities is both economically unsustainable and incongruent with public expectations, says a new report by the National Research Council.  The report says that tools already exist for BLM to better manage horses and burros on healthy ecosystems, enhance public engagement and confidence, and make the program more financially sustainable.  It also provides evidence-based approaches that, if widely and consistently implemented, can improve the management of these animals on public lands in the western U.S. 


The committee that wrote the report determined that most free-ranging horse populations are growing at 15 percent to 20 percent a year, meaning these populations could double in four years and triple in six years.  With no intervention by BLM, the horse population will increase to the point of self-limitation, where both degradation of the land and high rates of horse mortality will occur due to inadequate forage and water.  In addition, periodic droughts, many of them severe, in the western public lands cause immediate and often unpredicted impacts.  There is little if any public support for allowing these impacts on either the horse population or the land to take place, and both go against BLM’s program mission.  However, the current removal strategy used by BLM perpetuates the overpopulation problem by maintaining the number of animals at levels below the carrying capacity of the land, protecting the rangeland and the horse population in the short term but resulting in continually high population growth and exacerbating the long-term problem.


To manage horse populations without periodic removals, widespread and consistent application of fertility control would be required, the committee determined.  Three methods in particular -- porcine zona pellucida (PZP) and GonaCon™ for mares and chemical vasectomy for stallions -- were identified as effective approaches. 


“The committee recommended these approaches based on the evidence of their efficacy with other populations, notably the horses on Assateague Island, but cautioned that scaling up use of these methods to the larger and more disseminated horse populations in the western U.S. will be challenging,” said Guy Palmer, a veterinarian with Washington State University and chair of the study committee. 


The committee also strongly recommended that BLM improve and standardize its methodology to estimate population size, stressing the importance of accurate counts as the basis for all management strategies.  A large body of scientific literature suggests that the proportion of animals missed in current surveys ranges from 10 percent to 50 percent. 


Additionally, an examination of the genetics and health of population groups as well as of the range lands they occupy can be used to assure that both the animal populations and the ecosystem are being appropriately managed.  Developing an iterative process whereby public participants could engage with BLM personnel scientists on data gathering and assessment would increase the transparency, quality, and acceptance of BLM’s decision-making process.


The study was sponsored by the U.S. Bureau of Land Management.  The National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council make up the National Academies.  They are private, nonprofit institutions that provide science, technology, and health policy advice under a congressional charter.  Panel members, who serve pro bono as volunteers, are chosen by the Academies for each study based on their expertise and experience and must satisfy the Academies' conflict-of-interest standards.  The resulting consensus reports undergo external peer review before completion.  A committee roster follows.




Lorin Hancock, Media Relations Officer

Rachel Brody, Media Relations Assistant

Office of News and Public Information

202-334-2138; e-mail


Additional resources:


Project Website


Pre-publication copies of Using Science to Improve the BLM Wild Horse and Burro Program: A Way Forward are available from the National Academies Press on the Internet at or by calling tel. 202-334-3313 or 1-800-624-6242.  Reporters may obtain a copy from the Office of News and Public Information (contacts listed above).


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Division of Earth and Life Studies

Board on Agriculture and Natural Resources


Committee to Review the Bureau of Land Management

Wild Horse and Burro Management Program



Guy H. Palmer1 (chair)

Regents Professor of Pathology and Infectious  Diseases;

Jan and Jack Creighton Endowed Chair

  in Global Health; and


Paul G. Allen School for Global Animal Health

Washington State University

Cheryl S. Asa
Director of Research, and
Association of Zoos and Acquariums Wildlife Contraception Center
St. Louis Zoological Park
St. Louis

Erik A. Beever
Research Ecologist
U.S. Geological Survey
Bozeman, Mont.

Michael B. Coughenour
Senior Research Scientist
Natural Resource Ecology Laboratory
Colorado State University
Fort Collins

Lori S. Eggert
Assistant Professor
Department of Biological Sciences
University of Missouri

Robert Garrott
Department of Ecology
Montana State University

Lynn Huntsinger
Professor of Rangeland Management
Department of Society and Environment
University of California

Linda E. Kalof
Professor and Fellow
Oxford Centre for Animal Ethics
Michigan State University
East Lansing

Paul R. Krausman
Department of Ecosystem and Conservation Sciences
University of Montana

Madan K. Oli
University of Florida

Steven Petersen
Assistant Professor
Brigham Young University
Provo, Utah

David M. Powell
Research Associate
Department of Conservation Biology
Wildlife Conservation Society
Bronx Zoo
New York City

Daniel I. Rubenstein
Department of Ecology  and Evolutionary Biology
Princeton University
Princeton, N.J.

David S. Thain
Assistant Professor
Department of Agriculture, Nutrition, and Veterinary Science
University of Nevada




Kara N. Laney

Study Director



1 Member, Institute of Medicine