New wild horse fertility control effort underway

Wild horses in the Reveille herd in southern Nevada were among the first to be part of a new Bureau of Land Management initiative aimed at expanding the use of fertility control vaccines to slow population growth and protect wild herds from overpopulation. 

It’s called a “catch-treat-hold-release” operation, or CTHR, and its primary focus is to gather wild horses, treat them with a fertility control vaccine, hold them for a determined amount of time (approximately 30 days), provide a booster treatment and then release them back to the range. Twenty-nine mares were treated and released as part of the Reveille operation in August, the first CTHR gather.  

Horses released to the range from a trailer
Wild mares were treated with GonaCon-Equine fertility control vaccine and released back to the range in August. Find more information on the 2023 Reveille Wild Horse Gather

“One of the main challenges to conducting more fertility control for wild horses is getting the treatments to the animals,” said Scott Fluer, Deputy Division Chief for the Wild Horse and Burro Program. “Catch-treat-hold-release gathers give the BLM the opportunity to conduct a sustained and strategic fertility control program in places where we didn’t think we could before.”  

The BLM has, in the past, conducted fertility control as part of typical gather operations. However, those operations were primarily focused on reducing overpopulations by removing excess animals and placing them into private care. CTHR gathers, on the other hand, are primarily focused on herds that are at or near their appropriate management level. This allows the fertility control program to be more effective, since a greater portion of a herd can be treated and released. 

In addition to CTHR gathers, some wild horses also receive fertility control vaccines via ground darting. As of the date of this article, the BLM supports darting programs in more than a dozen herds across the West, usually with cooperation from volunteers and partners. However, not all herds are conducive to these programs. Ground darting efforts are typically most successful in areas where the animals can be routinely accessed, and in herds with animals that are more approachable due to human presence. 

READ: Top 5 Things to Know About Wild Horse Fertility Control

The wild horses of the Reveille herd roam more than a hundred thousand acres of rugged, remote terrain about 50 miles east of Tonopah, Nevada – a town of about 2,000 people. The herd management area ranges from large flat valley bottoms to steep mountains climbing to 9,400 feet. There are portions of four Wilderness Study Areas within the herd management area, which prohibit motorized vehicle use in the management of wild horses.

A horse in a chute receiving injection from syringe
Wild mare receiving a booster dose of the GonaCon-Equine vaccine prior to release back to the range.

The Reveille horses were treated with the fertility control vaccine GonaCon-Equine, which has been approved for use in wild horses to prevent pregnancy. The BLM has increased used of GonaCon-Equine to provide longer lasting contraception and reduce the need to handle the wild horses compared to other fertility control vaccines. After a mare receives a booster dose within 30 days of treatment, GonaCon-Equine may prevent pregnancy for approximately 4-5 years. 

BLM Staff

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