Horse numbers have historically been managed at the park through periodic (every three to four years) roundups, utilizing helicopters to herd horses to a handling facility. Removed horses are then sold at public auction. However, the park is exploring alternative methods for herd management, including:
- Contraceptives: In 2009, scientists from Colorado State University began a research program to evaluate the effectiveness of GonaCon® (an immunocontraceptive agent) for controlling reproduction in feral horses at the park. The research is complete, and results are encouraging.
- Low-Stress Livestock Herding: Low-stress techniques have been used since 2008 for gently herding escaped bison back onto park lands. Similar methods are effective at controlling the movement and capture of horses. The technique is currently under structured evaluation as a practice for horse capture.
- Corral Trapping: Corral traps are effective for capture of feral horses on other federal lands. During 2015, the park established a corral trap in an area that horses frequently visit. Though using bait (e.g. water and mineral blocks) is minimally effective at luring horses, the corral trap facilities are used in combination with low-stress herding to capture horses.
- Chemical Immobilization: Tranquilizer darts are widely used for wildlife capture. They allow managers to selectively handle individuals with minimal impact on other members of the population. Chemical immobilization is utilized to capture horses at the park, and this tool is under evaluation to ensure safety of the animals.
- Adoption Program: The park works with the General Services Administration (GSA) to transfer animals to private ownership.
- Genetics Research: Hair samples from horses are processed for mitochondrial DNA sequence at the University of North Dakota and for nuclear microsatellite data at Texas A&M University. Molecular data is used to evaluate the genetic diversity, ancestry, and demography of the herd to inform management decisions.