The Humane Society of the United States and the Humane Society Legislative Fund are noted champions for the protection and well-being of the nation’s wild horses and burros, and we have strong policy and practical commitments to the humane management of their herds on America’s Western ranges. We oppose the use of lethal methods to manage equine populations, and we oppose the sale of these animals for slaughter and human consumption.

Long-term solutions to the challenge of managing horse and burro herds will require effective fertility control application, strategic and non-lethal gathering of animals, rehoming to pasture facilities and strong adoption initiatives. We work closely with scientists and other stakeholders to conduct research and field trials to improve fertility control technology and methods, and we’re pushing the federal government to strengthen its own commitment to non-lethal management of the animals via fertility control and other methods.

Free-roaming horses and burros deserve every chance to live out their lives wild and free. If population management requires interventions, we must do everything possible to ensure those actions are in the best interest of the animals.

A complex challenge for an American icon

The Humane Society of the United States has long advocated for America’s wild horses and burros, starting in the late 1950s when we partnered with the legendary Velma Johnston (aka “Wild Horse Annie”) and other animal defenders to end the mass killings of wild horses and burros on public lands. Those efforts culminated in the enactment of the Wild Free-Roaming Horses and Burros Act of 1971 (P.L. 92-195), which banned lethal roundups of these living icons of the American West.

In the years since, the HSUS and the Humane Society Legislative Fund have continued to lobby, litigate and advocate on behalf of wild horses and burros, partnering with other groups to secure greater protections and more humane management of these animals. We’ve also played a crucial role in the development and implementation of humane contraception, a game-changing technology that is helping to mitigate and resolve human-wildlife conflicts around the world. 

Moving forward

In recent decades, disputes over the management of America’s wild horses and burros has created something of a political quagmire. To appease ranching interests, the federal Bureau of Land Management, a division of the Department of the Interior, has locked itself into an unsustainable cycle of removing horses and burros and warehousing them in holding facilities. Meanwhile, wild horse and burro populations have continued to grow both on the range and within holding facilities, even as the costs and political tensions surrounding the BLM program have increased, too.

In 2018, the U.S. House of Representatives voted to lift a longstanding prohibition on the killing of healthy wild horses and burros. This proposal failed in the Senate, but the House’s action sent a clear message: Legislators from both parties were frustrated by stakeholders’ refusal to work together toward a long-term management solution. If something didn’t change, and if stakeholders didn’t find common ground, the days of mass killings could soon return.

In response to this clear threat, the HSUS and HSLF came together with a group of diverse interests—including representatives from animal welfare, wild horse advocacy, conservation and rangeland management organizations, and expert consultants in ecology and economics—to identify the elements of a nonlethal management strategy for wild horses and burros. Participants agreed that with greater will, better planning and proper resources, the BLM could effectively manage wild horses and burros primarily through the use of fertility control vaccines. To reach that point, however, would take 10 years and require four key BLM commitments:

  1. Comprehensive large-scale application of safe, proven, humane and effective fertility control strategies to stabilize wild horse and burro populations.
  2. Targeted gathers of horses and burros in densely populated areas that cannot sustain large numbers, to protect animals from forage and water shortages and facilitate humane, nonlethal population management.
  3. Relocation of horses and burros currently in short-term holding facilities and those newly taken off the range to large, cost-effective, humane, free-roaming pasture facilities.
  4. Increased adoptions of wild horses and burros into caring families to improve the lives of those currently warehoused, reduce costs of the BLM program and redirect funds to long-term strategies for the humane and sustainable management of horse and burro populations.

This approach would revamp the BLM’s management framework by combining customary techniques and approaches with innovative strategies designed to minimize interference with animals on the range and set the stage for humane, long-term care and rehoming for those who are removed. (See our FAQs.)


We believe that the aggressive application of fertility control methods, including immunocontraception vaccines, must be at the heart of a long-term solution. We support immunocontraception as a humane, effective way to manage wild animal populations where active management is needed and justified. To facilitate its use, the HSUS has sponsored relevant research, forged active partnerships with public agencies, communities, parks, zoos and other entities, and conducted field studies across the United States. The HSUS has also worked with the BLM and the U.S. Forest Service to expand the use of the porcine zona pellucida immunocontraceptive vaccine (PZP) for managing wild horse and burro herds.

We are committed to increasing the number of available humane fertility control tools; with the BLM, we have supported research by Purdue University to develop a synthetic, longer-acting formulation of the PZP vaccine. We also joined with the BLM to conduct a pilot project to assess the feasibility of fertility control for management of the wild burro population in the Black Mountain Herd Management Area in northwestern Arizona.

Immunocontraception FAQ

Adoption Incentive Program (AIP)

The HSUS and HSLF have called on the BLM to immediately suspend its current adoption incentive program and authorize a thorough investigation following the publication of a May 2021 New York Times article. The article contains allegations that unscrupulous “adopters” are accepting taxpayer dollars, but instead of using the funds to care for these horses, they’re pocketing it and then selling these animals to slaughter. This is unacceptable if true. Our support of the BLM’s adoption program has been founded on it being true to both the letter and the spirit of these adoption agreements. We expect such cases are likely unusual in the broad scope of this program, but BLM must act decisively to investigate these allegations and correct the identified issues. Incentivized adoptions should not be allowed to serve as a slow-motion route to slaughter.

Surgical sterilization of mares

The HSUS and HSLF do not support surgical sterilization of mares because we do not believe it can be performed safely and humanely in the field (and the BLM has not provided evidence to show otherwise). Field implementation would require gathering and holding mares for significant periods of time for invasive surgery and post-op monitoring. Aside from the welfare concerns, the cost to taxpayers would be exorbitant. It would be better for the BLM to expand its use of less invasive, more cost-effective and proven fertility control tools on a scale necessary to manage wild horse and burro populations humanely and effectively.

For these reasons, the HSUS and HSLF oppose any efforts by Congress or the BLM to promote surgical sterilization as a population management method, including for mares in the Confusion Herd Management Area in Utah.

Helicopter-drive gathers

Immunocontraceptive vaccines, such as PZP, PZP-22 and GonaCon, can be administered by remote darting on the range or by hand-injection following humane capture. To effectively stabilize or reduce wild equine populations over time, a high proportion (>80%) of mares and jennies (female burros) must be treated. In some instances involving island herds and some BLM and U.S. Forest Service herds in which the animals are somewhat acclimated to people, it is possible to vaccinate high proportions of mares and jennies by locating individuals and delivering the vaccine via darting. However, because the vast majority of wild horses and burros on public lands are wary of people, scattered over enormous distances and frequently inhabit challenging terrain, darting will not be feasible for most females in these herds.

Where remote darting is not an option, the alternatives for capturing and treating wild horses and burros with fertility control vaccines are bait-trapping and helicopter-drive gathers. The HSUS is collaborating on studies in Arizona and elsewhere to explore how, where and when baited traps can be used to attract mares and jennies for administration of vaccines. While bait-trapping and other gather techniques are improving, helicopter-drive gathers are likely to play a role in the delivery of fertility control vaccines for the foreseeable future in order to reach a high enough proportion of the animals to stabilize and reduce their populations over time.

If the BLM chooses to rely upon helicopter-drive gathers, it has an ethical obligation to conduct them in a manner that reduces, to the greatest extent possible, the physical and emotional anguish that wild horses may endure during such operations. For this reason, we will continue to encourage and work with the BLM to expand and strengthen its Comprehensive Animal Welfare Program for Wild Horse and Burro Gathers, which “defines standards, training and monitoring for conducting safe, efficient and successful WH&B gather operations while ensuring humane care and handling of animals gathered.”

Removals and population management modeling

There are herd management areas where effective fertility control programs are underway and other HMAs where populations can be managed with fertility control tools alone. We continue to encourage the BLM to maintain and expand those programs. However, for the vast majority of the 177 HMAs managed by the BLM, there is no feasible way to decrease the growing number of excess wild horses and burros to sustainable levels solely using fertility control tools. The sheer numbers and locations of animals the agency would have to treat, the fiscal constraints under which the BLM must operate and the shared goal of the agency and Congress to see burgeoning population levels stabilized make such rapid progress impossible. Population management modeling demonstrates that only through a combination of techniques, used simultaneously, can managers stabilize populations without resorting to lethal methods such as slaughter and mass culls.

Appropriate management levels

While the HSUS and HSLF do not believe that the agency’s current “appropriate management level” or “AML” is properly supported by science, we recognize it is the legal framework that the BLM must work within. Changing this would require a legislative fix that is not politically viable right now. Despite years of pressure and promotion of alternative approaches by organizations and individual advocates, we have not been able to persuade agency officials, and Congress shares their view. At this point, given the desire by BLM and Congress to reduce the number of wild horses and burros on the range to closer to AML, in the absence of a longer-term humane solution, it is likely that slaughter and mass culling will result.

Setting aside the debate over what constitutes “too many” wild horses and burros on the range, our approach is based on the knowledge that on many HMAs, without intervention (including removals) to reduce the current on-range population, these animals are unlikely to experience humane outcomes given the current state of availability of forage and water on public lands.

Both the BLM and Congress are pushing for a significant decrease in the number of wild horses and burros on BLM lands. Our approach presents a nonlethal pathway toward a more responsible and humane wild horse and burro program. This requires lowering on-range population numbers closer to agency-determined “appropriate management levels” by removing and relocating some animals to more humane long-term care areas, stabilizing and reducing population growth rates on the range and increasing adoptions. Our fundamental goal is to help move the BLM strategy to the point where large-scale removals are a thing of the past and fertility control is the foundation of the BLM’s wild horse and burro management plan.