In 1971, the Wild Free-Roaming Horses and Burro Act was created in order to preserve what many consider a part of American history, wild horses. Before 1971 wild horse and burro populations were in decline across the United States, and legislation was needed in order to protect the herds that remained. The Act allowed the Secretary, in this case the Secretary of the Interior, to protect and manage wild horse populations in order to preserve ecological balance within their rangelands. Since the enactment of the Free-Roaming Wild Horse and Burro Act, populations have recovered well and are now at a point where management techniques need to be re-evaluated due to the fact that populations are doubling every four years. Recent studies have focused on fertility control methods to control population growth, while the current management techniques include frequent roundups, adoptions and disposal of old, sick or injured horses. The Act allows the Secretary to determine where there is excess animals, and determine what the best population control method is based on the most update information available. While the Bureau of Land Management is the primary agency that manages the wild horse populations, they work closely with other agencies in order to ensure rangeland health.
https://www.blm.gov/or/regulations/files/whbact_1971.pdf
