BLM, USGS Begin New Wild Horse Fertility Control Study

Straight from the Horse's Heart

Unedited Press Release from the BLM

The Bureau of Land Management and the United States Geological Survey (USGS) have begun a five-year wild horse contraceptive study at the BLM’s short-term holding facility in Pauls Valley, Oklahoma.  The pasture breeding study will test the effectiveness of two formulations of the investigational contraceptive vaccine SpayVac® to determine if the treatment can reduce foaling rates in wild horse mares.

The goal is to see if SpayVac®, a novel formulation of a glycoprotein called porcine zona pellucida (PZP), will provide a longer-term effect than other PZP vaccines currently used by the BLM.  If the vaccine is found to reduce foaling in this controlled setting, it will be considered for use with free-roaming horses to help control population growth rates on the range.

As the primary agency responsible for management of wild horses on U.S. public lands, the BLM has a need for a long-lasting contraceptive agent to control herd growth rates. Given the protection afforded by the Wild Free-Roaming Horses and Burros Act of 1971 and a general lack of natural predators, wild horse populations increase at an average rate of 20 percent a year and can quickly exceed the carrying capacity of their ranges.

The BLM, as part of its development of a new wild horse and burro management strategy, has been stepping up its efforts to reduce population growth rates in wild horse herds using contraceptive agents. A main limitation of the agents currently available is that they are of relatively short duration or need to be administered annually. Maximizing the duration of contraceptive effectiveness is especially important in wild horses, which in most cases must be captured in order for the treatment to be successfully administered.

In the BLM-USGS study, 90 mares have been treated with either one of two formulations of the vaccine or a placebo.  The mares will be followed for five years to measure anti-PZP antibody levels and compare the foaling rates between treated horses and controls.  Although breeding is not usually allowed to occur in BLM facilities, a clinical trial in this controlled environment will provide critical information on how well SpayVac® works as a contraceptive.

The mares and stallions enrolled in the study were selected from horses already in BLM holding facilities.  They are being housed in three 30-acre pastures and will be together during the next five breeding seasons.  Foals that are born during the study will be offered for adoption each fall after they have been weaned. At the conclusion of the study, all adult horses will be returned to the BLM’s Adopt-A-Horse Program or placed in long-term pasture facilities.

The BLM has an interagency agreement with the USGS for research and scientific support, and this study is a collaborative effort with scientists from the USGS, veterinarians with the Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS), and TerraMar Environmental Research LLC.
Contacts:           Paul McGuire     , 405-794-9624    
            Heather Emmons     , 775-861-6594    
            Tom Gorey     , 202-912-7420