43 C.F.R. § 4710.5 : Public Lands: Interior — REGULATIONS RELATING TO PUBLIC LANDS — BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR — RANGE MANAGEMENT (4000) — PROTECTION, MANAGEMENT, AND CONTROL OF WILD FREE-ROAMING HORSES AND BURROS — MANAGEMENT CONSIDERATIONS — Closure to livestock grazing

(a) If necessary to provide habitat for wild horses or burros, to implement herd management actions, or to protect wild horses or burros, to implement herd management actions, or to protect wild horses or burros from disease, harassment or injury, the authorized officer may close appropriate areas of the public lands to grazing use by all or a particular kind of livestock.
(b) All public lands inhabited by wild horses or burros shall be closed to grazing under permit or lease by domestic horses and burros.
(c) Closure may be temporary or permanent. After appropriate public consultation, a Notice of Closure shall be issued to affected and interested parties.

43 C.F.R. § 4710.5