The U.S. Department of Agriculture’s Wildlife Services’ National Wildlife Research Center announced on Feb. 13 that the U.S. Environmental Protection Agency granted regulatory approval for the use of GonaCon-Equine immunocontraceptive vaccine 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. We are pleased to be able to expand the vaccine’s application to include wild horses and burros,” said NWRC Director Larry Clark. “This non-lethal tool will provide another option to wildlife managers working to reduce overabundant wild horse and burro populations in the United States.”

However, the vaccination has only received federal approval; it must also be registered with the each individual state’s pesticide registration authority.

The Bureau of Land Management estimates approximately 37,300 wild horses and burros roam on BLM-managed lands in the western United States. This number exceeds by almost 11,000 the number the BLM has determined can be sustained in balance with other land uses. Additionally, the BLM cares for more than 49,000 wild horses and burros in pastures and corrals.

Currently, management for wild horses and burros include removing the horses and putting them up for adoption or holding them indefinitely. GonaCon-Equine was developed as a non-lethal means to control the wild horse population.

USDA public affairs specialist Gail Keirn explained that the vaccine is registered as a restricted-use pesticide because the EPA does not have a classification for contraceptives. The drug has been tested at the Virginia Range in Nevada and is currently being tested at the Theodore Roosevelt National Park in North Dakota.

The vaccine is currently manufactured by NWRC, but the WS program may at some point license the vaccine to a private manufacturer. Only those with appropriate authority over wild horse and burro management may use GonaCon-Equine.

The GonaCon-Equine vaccine stimulates the production of antibodies that bind to the gonadotropin-releasing hormone 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 hormones. All sexual activity is decreased, and animals remain in a non-reproductive state as long as a sufficient level of antibody activity is present. The product can be delivered by hand injection, jab stick or darting.