Contraceptive Vaccine for Wild Horses, Burros Gains EPA Registration

The USDA's Wildlife Services' (WS) National Wildlife Research Center (NWRC) announced Feb. 13 that the U.S. Environmental Protection Agency (EPA) has granted regulatory approval for the use of an equine immunocontraceptive vaccine (GonaCon-Equine) in adult female wild or feral horses and burros. GonaCon was developed by NWRC scientists and is the first single-shot, multiyear wildlife contraceptive for use in mammals.

"Since 2009, GonaCon has been available for use in female white-tailed deer," said NWRC Director Larry Clark. "We are pleased to be able to expand the vaccine's application to include wild horses and burros. This nonlethal tool will provide another option to wildlife managers working to reduce overabundant wild horse and burro populations in the United States."

The Bureau of Land Management (BLM) estimates that approximately 37,300 wild horses and burros (about 31,500 horses and 5,800 burros) roam on BLM-managed rangelands in 10 Western states. The estimated current free-roaming population exceeds by nearly 11,000 the number that the BLM has determined can exist in balance with other public rangeland resources and uses. Current management options are limited with the majority of actions involving the removal of horses and burros from the range and either offering them for adoption or holding them indefinitely in captivity. The BLM estimates there are more than 49,000 wild horses and burros off of BLM-managed lands that are fed and cared for at short-term corrals and long-term pastures.

The GonaCon-Equine vaccine stimulates the production of antibodies that bind to the gonadotropin-releasing hormone (GnRH) in an animal's body. GnRH signals the production of sex hormones (e.g., estrogen, progesterone, and testosterone). By binding to GnRH, the antibodies reduce GnRH's ability to stimulate the release of these sex hormones. All sexual activity is decreased, and animals remain in a nonreproductive state as long as a sufficient level of antibody activity is present. The product can be delivered by hand injection, jab stick, or darting.

GonaCon-Equine is registered as a restricted-use pesticide, and all users must be certified pesticide applicators or persons under their direct supervision. Only USDA-WS and Veterinary Services, U.S. BLM, U.S. Fish and Wildlife Service, U.S. National Park Service, U.S. Department of Defense, Federally recognized Indian Tribes, State agencies responsible for wild or feral horse and burro management, public and private wild horse sanctuaries, or persons working under their authority can use it. In order for GonaCon to be used in any given state, it must also be registered with the state's pesticide registration authority. Additionally, users are encouraged to contact their state fish and game/natural resource agency to determine specific State requirements. The vaccine is currently manufactured by NWRC; however, the WS program is interested in licensing the vaccine to a private manufacturer.

Future NWRC research with GonaCon will likely involve studies to support expanded registration to other species (e.g., prairie dogs and feral dogs) and aid in preventing the transmission of wildlife diseases.

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