Key Findings of the NAS Report on Wild Horse and Burro Management

June 9, 2013

AWHC Contributor

The National Academy of Sciences (NAS) report provides an in-depth analysis of the Bureau of Land Management's (BLM) practices regarding wild horse and burro management. It highlights the need for a scientific basis in decision-making, the importance of fertility control, and the necessity of public engagement. This article summarizes the key findings and recommendations from the report, offering insights into improving current management strategies.

BLM’s “Business as Usual” Unproductive

Continuation of “business as usual” practices will be expensive and unproductive for BLM and the public it serves.

BLM Lacks Scientific Rationale for Number of Horses Allowed on Range

The committee could not identify a science-based rationale used by BLM to allocate forage and habitat resources to various uses within the constraints of protecting rangeland health and listed species and given the multiple-use mandate.
How Appropriate Management Levels (AMLs) are established, monitored, and adjusted is not transparent to stakeholders, supported by scientific information, or amenable to adaptation with new information and environmental and social change. Standards for transparency, quality, and equity are needed in establishing these levels, monitoring them, and adjusting them.
Environmental variability and change, changes in social values, and the discovery of new information require that AMLs be adaptable.
AMLs are a focal point of controversy between BLM and the public. It is therefore necessary to develop and maintain standards for transparency, quality, and equity in AML establishment, adjustment, and monitoring.

BLM Under Utilizes Fertility Control

According to BLM’s presentation to the committee, the agency treated an average of 500 mares a year with the porcine zona pellucida (PZP) vaccine from 2004 to 2010; just over 1,000 were treated in 2011. Contracepting 500-1,000 mares a year with a 2-year vaccine will not substantially lower the rate of growth of a population of over 30,000 horses.

Immediate Action More Affordable: Tools Exist to Address BLM Challenges

Tools, including PZP fertility control, already exist for BLM to address many challenges. The report confirms that BLM is not using PZP in a manner that will impact population growth.
In the short term, more intensive management of free-ranging horses and burros would be expensive. However, addressing the problem immediately with a long-term view is probably a more affordable option than continuing to remove horses to long-term holding facilities.

Most Promising Fertility Control: PZP, GonaCon, and Chemical Vasectomy

On the basis of the peer-reviewed literature and direct communication with scientists who are studying fertility control in horses and burros, the committee considers the three most promising methods of fertility control to be PZP-22, GonaCon, and chemical vasectomy.
To the extent that GonaCon preserves natural behavior patterns while effectively preventing reproduction, it is a promising candidate as a female-directed fertility-control method. However, further studies of its behavioral effects are needed.
Most promising fertility-control methods for free-ranging horses or burros are porcine zona pellucida (PZP) vaccines and GonaCon™ vaccine for females and chemical vasectomy for males. This conclusion is based on criteria such as delivery method, availability, efficacy, duration of effect, and potential for side effects. Although applying these methods usually requires gathering horses and burros, that process is no more disruptive than the current method of population control — gathering and removal — without the further disruption of removing animals. Considering all the current options, these three methods, either alone or in combination, offer the most acceptable alternative to removing animals for managing population numbers.

BLM Roundups Increase Horse Populations

Management practices are facilitating high rates of population growth. Thus, population growth rate could be increased by removals through compensatory population growth from decreased competition for forage. As a result, the number of animals processed through holding facilities is probably increased by management.
Free-ranging horse populations are growing at high rates because their numbers are held below levels affected by food limitation and density dependence.

Burros: Current Estimated Population Should Not be Reduced

In most HMAs managed for populations of burros, 2012 AMLs were exceeded. However, the total population of burros is much smaller than that of horses; in 2012, BLM reported 5,841 burros in HMAs. That number needs to be verified with appropriate survey methods, but if it is accurate, removing burros permanently from the range could jeopardize the genetic health of the total population. The burro population is more fragmented than the horse population. Burro HMAs exist in five states; no state-aggregated AML exceeds 1,500 burros; and the cumulative, program-wide AML for burros is 2,923. Translocation of burros between HMAs would need to occur more often than it would for horses to compensate for the geographic fragmentation and small size of the population. BLM may also need to assess whether the AMLs set for burros can sustain a genetically healthy total population.
BLM may also need to assess whether the AMLs set for burros can sustain a genetically healthy total population.

Social Considerations

Horse and burro management and control strategies cannot be based on biological or cost considerations alone; management should engage interested and affected parties and also be responsive to public attitudes and preferences. Three decades ago, the National Research Council reported that public opinion was the major reason that the Wild Horse and Burro Program existed and public opinion was a primary indicator of management success. The same holds true today.
In 1982, the National Research Council noted that public opinion was the “major motivation behind the wild horse and burro protection program and a primary criterion of management success,” suggesting that control strategies must be responsive to public attitudes and preferences and could not be based only on biological or cost considerations.
Thus, BLM should engage with the public in ways that allow public input to influence agency decisions, develop an iterative process between public deliberation and scientific discovery, and co-design the participatory process with representatives of the public.
BLM has involved the public in a consultative way in the past, but to move toward a collaborative process, BLM and the public must come together to work in new ways and with a new spirit.
A participatory adaptive-management process for the setting and adjustment of AMLs, for example, might involve testing the effects of different herd levels on wildlife habitat. With the objective of meeting the stipulation of the Wild Free-Roaming Horses and Burros Act of 1971 (as amended) to protect wildlife, stakeholders—including scientists, the public, and managers—could decide on an AML to be tested, examine together the outcomes of monitoring (or even participate together in monitoring), and, on the basis of the results, propose adjustments of the AML.
Adaptive management could provide much-needed transparency for BLM’s management of free-ranging horses and burros. Because it is a flexible system, it allows managers to experiment with a variety of policies and actions to determine which provide the desired management outcomes. That could be particularly useful for BLM, given the number and variety of stakeholders involved in this issue. BLM could implement “experimental” policies to determine whether they produce desired outcomes. Later, management actions could be adapted on the basis of the previous outcomes, and BLM could provide a clear view of its practices to stakeholders.

Ovariectomy (Spaying) and Gelding Not Recommended

The possibility that ovariectomy may be followed by prolonged bleeding or peritoneal infection makes it inadvisable for field application.
However, some or total loss of sex drive would be likely in castrated stallions, and this is counter to the often-stated public interest in maintaining natural behaviors in free-ranging horses. With respect to effects at the population level, it is not clear how castration of males would be better than vasectomy, which does not affect testosterone or male-type behaviors. Ultimately, the growth rate of any population that includes reproductive horses of both sexes will be commensurate with the number of fertile females in the population.
A potential disadvantage of both surgical and chemical castration is loss of testosterone and consequent reduction in or complete loss of male-type behaviors necessary for maintenance of social organization, band integrity, and expression of a natural behavior repertoire.
The possibility that ovariectomy may be followed by prolonged bleeding or peritoneal infection makes it inadvisable for field application.

Chemical Vasectomy

For population control, a more effective approach would be to vasectomize a larger proportion of males, regardless of age or social status. The target number or proportion of males treated could be adjusted to achieve the level of population control recommended for each HMA.
Chemical vasectomy is a simpler, less invasive alternative to a surgical approach, but both require anesthesia. Several chemical agents have been assessed in domestic dogs and cats. There are no published reports on chemical vasectomy in horses, but the procedure should not be difficult to adapt.