Fertility Control: Humane Management of Wild Horses
Porcine Zona Pellucida (PZP) is a fertility-control vaccine administered to female horses on the range via remote darting. With over three decades of proven use, PZP is recommended by the National Academy of Sciences for federally protected wild horse herds. It offers a humane alternative to roundups and removals, presenting the most promising strategy for managing wild horses in their natural habitat.
Why the Need for Fertility Control?
Wild horses in the United States are confined to Herd Management Areas (HMAs) or Wild Horse Territories (WHTs) on public lands managed by the Bureau of Land Management (BLM) or U.S. Forest Service (USFS). These lands are used for various commercial and recreational purposes. Predators like mountain lions and wolves are not present in sufficient numbers to regulate wild horse populations due to hunting and government predator control programs.
The BLM is tasked with managing public lands for multiple uses without allowing range deterioration. Unmanaged, wild horse populations might stabilize at their ecological carrying capacity, but this would lead to unsound ecological conditions.
America's mustangs face unnatural conditions due to genetic manipulation and behavioral disruption from roundups and removals. Fences confine them to artificial habitats, inhibiting their natural migration. They compete with other land uses backed by powerful economic interests, making natural regulation impractical.
The American Wild Horse Conservation (formerly American Wild Horse Campaign) aims to secure fair resources for wild horses and protect predators to restore ecological balance. However, managing wild horse population growth is necessary. PZP fertility control is the most humane, minimally intrusive method available today.
What is PZP?
The PZP vaccine, registered with the EPA as ZonaStat-H, has been used in multiple wildlife species, including wild horses. It induces an immune response that prevents fertilization without affecting hormone production, thus preserving natural behaviors. The vaccine is reversible and effectively manages wild horses in the U.S., as demonstrated in programs like Assateague Island National Seashore and McCullough Peaks HMA.
How Does it Work?
PZP is administered via a dart injected at the hip, which is then retrieved. It prevents fertilization through an immune response without affecting the horse's hormonal system, preserving natural behaviors. Safe for pregnant and nursing mares, PZP requires an initial primer dose followed by a booster two weeks later, and can be used on horses as young as 11 months.
Is PZP Expensive?
No, a dose of PZP costs $30, significantly less than the $2,800 annual cost of warehousing a horse. Initial costs include training and dart gun purchase, but program costs decrease over time. Allocating just 5% of the BLM's program budget to PZP could substantially reduce long-term holding costs.
PZP is “a more affordable option than continuing to remove horses to long-term holding facilities.”
- National Academy of Sciences, 2013
"PZP use with select removals could save about $8 million over 12 years in one Herd Management Area alone."
- de Seve and Griffin, Journal of Zoo and Wildlife Medicine, 2013
Is it Difficult to Locate the Horses?
PZP programs are tailored to specific herds, considering herd dynamics and geography. Darting teams track horse movements and identify horses needing booster vaccines using markings and photography. The American Wild Horse Conservation's Virginia Range Program maintains a scientific database updated by field photographers. Drones and game cameras assist in locating remote bands, eliminating the need for helicopter roundups.
The Virginia Range program covers a 300,000-acre area in Nevada, demonstrating successful fertility control implementation. Learn more about the Virginia Range Fertility Program.
What’s the Main Barrier to Using PZP?
The BLM has not voluntarily adopted PZP, relying instead on ineffective mass roundups and removals. Congress should mandate PZP use, directing the BLM to collaborate with organizations, purchase necessary equipment, and support training. PZP works effectively when properly implemented across public lands.
- Spring Creek Basin, Colorado: PZP has stabilized the wild horse population at 62 since 2012, with no removals since 2011.
- McCullough Peaks, Wyoming: Zero population growth achieved in 2015 with PZP, and no removals since 2013.
- Pryor Mountains, Montana: The BLM is nearing the elimination of wild horse removals due to PZP use.
FAQ:
Will It Be Difficult to Treat All of The Horses in the West? No, not all horses need treatment. Only mares are treated, and PZP programs can start in areas with approachable horses and volunteer support. Effective implementation requires BLM support and specific plans for each HMA.
Is PZP Effective? Yes, PZP is highly effective, with a 95-97% efficacy rate. Studies show mares treated for 5-7 years may self-boost, reducing the need for additional treatments.
Is PZP a pesticide? No, PZP is an immunocontraceptive vaccine registered under the EPA's pesticide category due to bureaucratic reasons. It is produced by the Science and Conservation Center and provided at a financial loss.
Additional resources on PZP for fertility control: