Contraceptive for wild horses gets regulatory nod

Wild horses running free.
Wild horses running free. © Cynthia Smalley

Regulatory approval has been granted by the US Environmental Protection Agency for the use of the long-acting contraceptive GonaCon in female wild horse and burros.

GonaCon is the first single-shot, multiyear wildlife contraceptive for use in mammals.

Approval was sought by the US Department of Agriculture’s Wildlife Services’ National Wildlife Research Center (NWRC), which developed the vaccine.

“Since 2009, GonaCon has been available for use in female white-tailed deer,” NWRC Director Larry Clark said.

“We are pleased to be able to expand the vaccine’s application to include wild horses and burros.

“This non-lethal 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 estimates about 37,300 wild horses and burros (about 31,500 horses and 5,800 burros) are roaming its managed rangelands in 10 Western states.

The estimated current free-roaming population exceeds by nearly 11,000 the number that the bureau 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 from bureau-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, such as 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.

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

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