BLM studies one-dose fertility control for wild horses and burros

The Bureau of Land Management and partners will study the effectiveness of a fertility control vaccine that works in just one dose in feral horses previously removed from the wild.

Last week, the BLM released an Environmental Assessment for the study, which they will conduct in partnership with the U.S. Department of Agriculture Animal and Plant Health Inspection Service’s National Wildlife Research Center (NWRC).

The vaccine, which includes an oocyte growth factor for fertility control, may eventually be used in legally designated wild horses and burros managed by the agency under the Wild and Free-Roaming Horses and Burros Act.

Populations of the ecologically feral species have steadily increased well beyond sustainable levels in recent years. As of March, more than 88,000 horses and burros managed by the BLM inhabited public lands — more than three times the population goal of less than 27,000 individuals. The BLM is mandated by law to control the populations, but policy restrictions limit the agency’s ability to manage them. The Wildlife Society has regularly advocated for federal agencies to reduce populations of free-roaming horses and burros on public land, where the invasive species can compete with native wildlife and damage habitat.

The draft EA, released last week, calls for a research study in which 16 mares are given the vaccine and held in pens — each pen will house four mares and one stallion. The researchers will assess the effectiveness of the fertility control in these horses for three years. A control group of 16 untreated mares would similarly be held in pens for the duration of the study.

While the long timeline is necessary to analyze what project leads hope is a long-lasting fertility control vaccine, the project length is also a source of concern. “We applaud the efforts of the BLM and its partners to explore fertility control options, but at the same time urge immediate action to control wild horse and burro populations and return ecological balance to our public lands,” said Caroline Murphy, AWB®, government relations manager at The Wildlife Society.

The NWRC has previously studied other versions of the oocyte growth factor vaccine, which required multiple doses and prevented fertility for two years. The BLM currently uses multi-dose fertility vaccines, such as porcine zona pellucida, or PZP, which only lasts for about a year.

The National Wild Horse and Burro Advisory Board met earlier this fall and issued a series of recommendations on wild horse and burro management, including that the BLM continue to explore options for long-term fertility control.

Public comments will be accepted on the draft EA until Dec. 19.

Read TWS’s Issue Statement on Feral Horses and Burros in North America.