Wild horses, often called Mustangs, are an enduring symbol of the American West, freely roaming vast stretches of public land. These animals are not native species, but descendants of domesticated horses brought to the Americas centuries ago. They are considered an introduced, free-roaming population with deep cultural significance, especially in states like Utah. Their presence is protected by federal law, which mandates that the government manage and preserve them on designated rangelands. This management requires balancing the preservation of the horses and maintaining the health of the delicate desert ecosystems they inhabit.
Current Population Counts and Management Goals
The number of free-roaming horses in Utah is considerably higher than the land can sustainably support. As of March 1, 2024, the estimated population on Bureau of Land Management (BLM) administered lands was approximately 4,407 animals. This figure includes horses found both inside and outside of their designated management areas.
This current population is measured against the Appropriate Management Level (AML), which is the science-based target range for a healthy, thriving population. The AML is determined by assessing the forage, water, and habitat available, ensuring that the horses can coexist with native wildlife and other authorized land uses.
For all of Utah’s Herd Management Areas combined, the established AML is 1,956 animals. The difference indicates an overpopulation of approximately 2,451 horses in the state. Wild horse populations can increase rapidly, often doubling their numbers every four years. When populations exceed the AML, the competition for limited resources can lead to degraded rangeland health and put the horses at risk of starvation and dehydration.
Designated Herd Management Areas in Utah
Wild horses in Utah are managed within specific geographical boundaries known as Herd Management Areas (HMAs). An HMA is a designated area of public land where wild horses are allowed to roam freely under federal protection. Utah has 19 such HMAs, covering nearly 2.5 million acres of public rangeland across the state.
These areas provide spatial context for the state’s wild horse population, ranging from the remote western deserts to the central mountains. Well-known HMAs include the Onaqui Mountain HMA, located west of Salt Lake City, and the Sulphur HMA in the southwestern part of the state. Other significant areas are the Cedar Mountain, Confusion, and Sinbad HMAs.
The size and topography of these HMAs vary greatly, influencing the specific management challenges for each herd. For instance, the Frisco HMA, located in Beaver County, has a low AML of 30 to 60 animals, reflecting the limited forage in its pinyon-juniper dominated high-elevation terrain. Conversely, HMAs in the more open Great Basin country may have larger AMLs.
Federal Oversight and Population Control Methods
The management, protection, and control of wild horses on public lands fall under the jurisdiction of the Bureau of Land Management (BLM), a federal agency. This responsibility is rooted in the Wild Free-Roaming Horses and Burros Act of 1971, which declared these animals to be living symbols of the historic and pioneer spirit of the West and requires their preservation. The BLM’s primary directive is to maintain the herds in a thriving ecological balance with the range, which necessitates active population control to stay within the AML.
One of the main operational methods for population control is the use of “gathers,” also known as roundups, which remove excess animals from the range. These operations typically employ helicopters to herd the wild horses into temporary corrals. The animals are then transported to off-range facilities, such as the contract facility in Axtell, Utah, where they receive veterinary care and are prepared for the BLM’s adoption and sale program.
Gathers are a necessary tool when the population significantly exceeds the AML. While effective at reducing immediate numbers, gathers are costly and controversial, and they do not prevent future population growth. This has driven the need for non-lethal, long-term solutions.
Fertility control is increasingly used as a management tool to slow the growth rate of herds while keeping them on the range. The most common method involves the use of the Porcine Zona Pellucida (PZP) vaccine, a reversible contraceptive delivered via a dart gun or administered during a gather. PZP works by stimulating the mare’s immune system to block fertilization, effectively preventing pregnancy for up to one to two years with a single dose.
Another option is GonaCon, a longer-lasting contraceptive vaccine that can provide multiple years of infertility. The application of these contraceptives is a targeted effort, often focusing on mares that are gathered and then released back onto the range. By treating a significant percentage of mares, the BLM aims to reduce the annual foaling rate, helping to stabilize herd sizes and prevent the population from rapidly exceeding the Appropriate Management Level again.