The Black Rock Field Office to release Calico Complex mares treated with fertility control

WINNEMUCCA, Nev. – The Black Rock Field Office concluded the Calico Complex wild horse gather near Gerlach, Nevada on October 1, 2022. 

The contractor gathered and removed 863 excess wild horses and removed 837 excess wild horses from public lands. GonaCon, Aa population suppression control vaccine, was administered to 39 mares. The mares will get a second dose within approximately 30 days of the first dose and then be released back to the Calico Complex.

On or about December 13, 39 mares will be released back to the range within the Calico Complex. Members of the public are welcome to view the release operations, provided that doing so does not jeopardize the safety of the animals, staff, contractors and observers, or disrupt release operations. Agency staff will escort the public to gather observation sites located on public lands. If you would like to view the release of the mares, please RSVP to for the meeting location and time.

“The agency’s top research priority remains the development of safe, practical, effective and long-lasting fertility control methods for wild horses and burros,” said Black Rock Field Office Assistant Manager, Andy Boerigter.

The purpose of the gather was to prevent undue or unnecessary degradation of the public lands associated with excess wild horses, to restore a thriving natural ecological balance and multiple-use relationship on public lands, consistent with the provisions of Section 1333(b) of the 1971 Wild Free-Roaming Horses and Burros Act. By balancing herd size with what the land can support, the wild horse staff aimed to address resources issues related to drought and past fire damage and protect habitat for other wildlife species such as sage grouse, pronghorn antelope and mule deer. Removing excess animals will enable significant progress toward achieving the Standards for Rangeland Health.

Gather reports and additional information for the Calico Complex Wild Horse Gather were posted on the BLM website at

The BLM manages more than 245 million acres of public land located primarily in 12 western states, including Alaska, on behalf of the American people. The BLM also administers 700 million acres of sub-surface mineral estate throughout the nation. Our mission is to sustain the health, diversity, and productivity of America’s public lands for the use and enjoyment of present and future generations.

Release Date


Bureau of Land Management


Black Rock Field Office


Heather O'Hanlon