Congress Requires a Review of the BLM Program on Wild Horses and Burros


The BLM LogoThe Bureau of Land Management (BLM) provides this report, as requested by Congress in the Consolidated Appropriations Act of 2019 (Appendix A), to identify “factors for success, total funding requirements, and expected results” to improve management of wild horses and burros. This report also responds to the reporting requirements accompanying the Further Consolidated Appropriations Act of 2020, so that BLM may obligate the full amount of its appropriation. The BLM’s multiple use mission and commitment to stewarding healthy, working landscapes across the western United States provide the foundation for all the recommendations in this report. The report is further informed by a historical context that reveals an escalating challenge and the need for decisive action to reverse the harm to western landscapes and the wild horses and burros occupying them. The harm inflicted on public lands from excess wild horses and burros compounds yearly as on-range population growth rates and off-range holding costs outstrip the BLM’s ability to manage herds according to the intent of the Wild Free-Roaming Horses and Burro Act of 1971, as amended.

Emphasis Block 1The BLM created the Wild Horse and Burro Program to implement the Wild-Free Roaming Horses and Burros Act. Broadly, the law declares wild horses and burros to be “living symbols of the historic and pioneer spirit of the West” and stipulates that the BLM and the U.S. Forest Service have the responsibility to manage and protect herds in their respective jurisdictions within areas where wild horses and burros were found roaming in 1971. In addition, they were mandated to sustain a thriving natural ecological balance and multiple use as the framework for determining any actions proposed to manage them.

In addition to removals and private care placements, the BLM spent time and effort looking into available fertility control vaccines and working with partners to develop new vaccines. The 1970s and 1980s were mainly dedicated to testing and developing these vaccines. By the early 1990s, the BLM began on the ground use of available vaccines in Nevada and expanded to other States throughout the 1990s. The wide-scale use of these population growth suppression methods was limited due to funding constraints.

As of March 1, 2019, the BLM estimates a minimum population of slightly more than 88,000 wild horses and burros within the 177 Herd Management Areas (HMA) on public lands. This number is more than three times higher than the national total AML of 26,715, with more than 80 percent (146) of the 177 HMAs now exceeding AML. If nothing were done to reduce the annual growth rate of these herds, by 2040, the BLM estimates the on-range populations of wild horses and burros could increase to over 2.8 million.

HERD SIZEBased on survival rates, fertility statistics, lifespan (20-30 years old on the range), the current on-range population levels, and the program funding levels assumed in this report (which limits, for example, how many animals can be removed and held), the BLM estimates that wild horse and burro herds will continue to grow for the initial four to six years after this plan is enacted. For the subsequent twelve to fifteen years, as a result of population growth suppression, removals, and private care placements proposed in this report, wild horse and burro herds would decrease significantly as off-range holding increases. After about a decade of large-scale actions, the BLM’s efforts would be devoted to reaching AML between years 15 –18 through a more focused and tailored approach to each HMA.

The following specific actions may be required over the next fifteen to eighteen years to implement the strategy described above.

• Annually gather (through both helicopter and bait/water trap methods) between 20,000 and 30,000 animals, and either remove them permanently from public rangelands or return them after application of some form of long-term temporary or permanent fertility control;
• Annually remove 18,000 to 20,000 animals permanently from public rangelands (placed into off-range holding) until AML is achieved;
• Treat (using various temporary long-term or permanent fertility control methods) 3,500 to 9,000 gathered animals annually over the initial 10 years from the time the strategy is enacted, slowly decreasing the number receiving the treatment in the last five years of the strategy;
• Annually place an estimated 6,000 -7,000 animals into private care;
• Procure additional off-range corrals (especially for preparatory activities) and off-range pastures to care and feed for the increased number of animals removed from the range;
• Streamline transportation logistics for movement of animals;
• Identify partner organizations able and willing to facilitate private care placements and house/care for as many of the 18,000-20,000 permanently removed off-range animals as possible; and
• Continue research into improving long-term fertility control treatments and humane permanent sterilization (with a particular emphasis on modern chemical sterilization methods).

Other topics explained in the PDF link

Off-range Pastures
Resource Monitoring
Population Surveys
Herd Management Area Plan Development
Rangeland Restoration and Rehabilitation
Program Management and Oversight


Wild Horses 3Removals with wild horse and burro populations in most HMAs far exceeding AML, removals that exceed the annual foal recruitment (i.e., birth) rate, sustained over several years, is the only effective way to immediately reduce populations. This analysis assumes annual removals of 18,000 –20,000 wild horses and burros after an initial year of increasing capacity as further described in this strategy and until AML is achieved. The BLM utilizes two main methods of gathering animals: helicopter and bait/water trap.

HMAs that are at or near AML. However, in HMAs where the population is far above AML, multiple gathers over several years would be necessary to achieve AML. In these cases, it is more effective to simply remove as many animals as can be gathered. Once these HMAs reach or are close to AML, then fertility control treatments can be employed more effectively to maintain AML. This is true for two main reasons:

• Most gathered mares are pregnant and even if treated will still give birth to that foal. This would add an animal to the on-range population (half of which would be breeding mares in just a couple years) even if that same mare were gathered or re-treated in a future year; and

• Without first getting close to AML, emphasizing fertility control would significantly prolong the number of years it takes the WHB Program to achieve AML, thus increasing costs for the on-range management activities into the future. As long as wild horse and burro populations on most HMAs far exceed AML, increased removals are the best method of immediately reducing population toward achieving AML. With animals living to 20-30 years old on the range, even a non-reproducing herd that is 100 percent above AML could take 15 or more years to reach AML through natural mortality alone.

REMOVALS: Factors to Success

To remove the number of animals to meet the objectives under this analysis, the BLM would need to:

• Increase the number of corral facilities by 3-4 with about 8,000 new spaces (this includes facilities/spaces potentially added through FY2020 solicitation), with appropriate personnel (2-3 employees per new corral), to receive animals removed from the range and prepare them for adoption, sale, or holding;
• Annually increase the amount of long-term pasture holding space by about 12-14,000 in the first six years, then about 9-11,000 until AML is achieved;
• Increase the number of contractors that perform gathers (both helicopter and bait/water/trap) by 2-3 to a total of 8-9 contracted employees;
• Provide additional removal support staff from other BLM support staff (15-20 additional, including Law enforcement, Public Affairs, Wild Horse Specialists, etc), such as dedicated contracting officers (2-3 additional); and
• Increase other BLM personnel to support gather operations, staffing for transportation logistics, and other key areas (see Pastures and Corrals sections for new staffing requirements indirectly related to removals).


Temporary fertility control methods used by the BLM for animals on the range are mainly vaccines. The BLM has relied primarily upon Porcine zona pellucida (PZP), which has a 90 percent efficacy rate, but is only effective for one year. Therefore, mares must be treated every year to remain infertile. Recently, the BLM has been funding research into the effectiveness of the vaccine GonaCon. It has an efficacy rate of 30-40 percent in the first year; however, if a booster is applied within 6-18 months of the initial treatment, its efficacy rate increases up to 90 percent for the next 4-5 years. This would result in an estimated cost of about $12,000 to keep a mare infertile for a lifetime using this vaccine and assuming that the mare could be re-captured every 5 years.

To apply the booster, the BLM may either re-gather the treated mares or hold them for at least six months and then apply the booster. Although the BLM will continue to use PZP, especially where darting of PZP occurs and has shown to be successful, the BLM plans to significantly expand the use of GonaCon. This approach represents an excellent example of research investments leading to future year savings. As such, the BLM continues with research into this critical component of on-range management. As new and innovative solutions to population control suppression become available through this research, the BLM will implement them as appropriate. These innovations could help drive down long-term costs by reducing the need for multiple gathers.


To implement an effective temporary fertility control program, the BLM would:

• Increase the number of contractors that can perform gather operations (2-3 contract employees to as many as 9 contract employees);
• Add support from other BLM staff outside the Program, such as dedicated contracting officers (15 to 29 additional employees);
• Contract with vendors to complete timely NEPA requirements (potentially between $500,000 to $1 million annually);
• Increase other BLM personnel to gather operations, staffing for transportation logistics, and other key areas; and
• Contract with providers to increase dosage production of the required vaccines (from about $30,000 annually to about $400,000 annually for the vaccine doses only).

Expected Results: The wide-scale application of PZP and GonaCon, or other longer-term fertility control vaccines, in concert with the large number of removals will begin the slow process of stabilizing, then reducing populations on the range. Using only short-term fertility control vaccines at any scale, however, will not significantly reduce the on-range population.


While gelding (i.e., castration) is used on virtually all stallions removed from the range, it is rarely used as a population growth suppression technique for herds on the range. Due to the reproductive nature of wild horses and burros, over 80 percent of males in a herd would have to be gelded to stabilize population growth. Permanently sterilizing females is the most effective growth suppression method; one treatment results in a lifetime of infertility. Thus, permanent sterilization is a better financial and more humane solution than long-term temporary fertility control growth suppression that require repeated gathers. At the same time, the BLM recognizes that in order to achieve a thriving natural ecological balance, it is important to balance stability in population with herd genetics and habitat health.


The BLM is prohibited from euthanizing healthy wild horses and burros by the annual Department of the Interior appropriations acts.


The BLM is prohibited from implementing a strategy to include sales of wild horses and burros without limitation by the annual Department of the Interior appropriations acts.


On-Range and Off-Range PopulationsThe BLM has two different types of off-range corrals: preparatory and maintenance. Preparatory facilities receive animals directly from the range. The animals become acclimated to living off the range; receive vaccine and dewormer treatments; obtain their identifying freezemark and/or microchip; and stallions are gelded in these facilities. With up to 70 percent of the mares removed from the range being pregnant, their foals are added to the off-range population total. In order to accommodate the level of removals in achieving AML, the BLM must have preparatory facilities in key locations throughout the West. In addition, preparatory facilities often perform the same function as maintenance facilities. Acquiring more preparatory facilities, in key western locations, will be essential if BLM is to remove the number of animals proposed in this strategy.

OFF RANGE: Factors for Success:

For the BLM to acquire enough space to accommodate all the animals proposed for removal, the BLM would need to:

• Increase the number of staff and partners in BLM-operated facilities (10-12 additional employee), staff that oversee contracted facilities, and inspection officers;
• Add support from other BLM staff, such as dedicated contract and grant officers (1 additional employee); and
• Release new solicitations annually that would attract facility owners who are willing and able to care and house wild horses and burros.

Conclusion BLM’s management activities require continued focus, improvement, and innovation to reverse declining rangeland health conditions on portions of the 25 million acres of public land now occupied by wild horses and burros. Surrounding lands may also be at risk, as animals lacking water or forage migrate to adjacent State, private, Tribal, or other Federal lands. With this migration would come increased safety concerns, such as animal incursions onto highways and even into private housing subdivisions where they may pose a risk to public safety. In addition, increased horse and burro populations impact other wildlife. For example, riparian areas that are used by multiple species, including wild horses and burros, will see further degradation. This can already be seen throughout the west, where vegetation has been lost or converted, as shown in the following photos in Nevada:

In other cases, much of the vegetation can be severely depleted from an area, such as in Antelope Valley, as can be seen in the photos below:

While these examples involve rangeland with high wild horse and burro populations, similar disturbing impacts would expand to lands throughout the West as populations in all HMAs grow exponentially, eventually into areas outside the current HMA boundaries.