Minimally Reproducing, Self-Sustaining Herds
Under the Wild Free-Roaming Horses and Burros Act of 1971, the BLM is required to maintain herd populations at appropriate management levels (AMLs) and protect the range from deterioration from overpopulation. The BLM is directed to determine whether appropriate management levels should be achieved by removal or humane destruction of excess animals or other options (such as sterilization or natural controls on population levels).
Consistent with that mandate and authority, the BLM can apply temporary or permanent sterilization to decrease herd growth rates while maintaining a herd's ability to sustain itself.
Achievement of a minimally reproducing herd is influenced by the proportion of the herd that can be gathered, treated, and released.
When implementing this type of population growth suppression, animals can be captured, sterilized, and returned to the range. Castration (gelding) is a safe, effective, humane, and efficient method of sterilizing stallions. It remains to be seen whether spaying mares can be done in a similarly safe, effective, humane, and efficient manner. For this reason, the BLM has focused on returning geldings to HMAs at this time.
Spaying and other means of sterilizing mares are being considered by the BLM but have not yet been applied as a management tool on the range.
If population numbers fall below AML in minimally reproducing herds, the BLM can bring in wild horses from other HMAs having similar environments. New animals can be introduced near resident animals in areas with abundant water and forage to facilitate their adaptation to a new area.