The BLM uses freezemarking to identify wild horses and burros that have been gathered from the public rangelands because of overpopulation. Freezemarking is a permanent, unalterable, and painless way to identify each horse as an individual. It is applied on the left side of the neck. It follows the International Alpha Angle System, which uses a series of angles and alpha-symbols that cannot be altered. The mark contains the Registering Organization (U.S. Government), year of birth, and registration number.

The technique is simple and completely painless to the animal. The left side of the neck is shaved and washed with alcohol, and the mark is applied with an iron that is chilled in liquid nitrogen. The hair at the site of the mark will grow back white and show the identification number.

In addition to the freezemark on the left side of the neck, sanctuary mustangs are marked on the left croup with four inch-high Arabic numerals that correspond with the last four digits of the freezemark on the neck.

Although every effort is made to apply freezemarks that are legible, occasionally freezemarks do get blurred. This happens when the iron is applied: the animal moves and all or some of the identification number cannot be read. It can also be difficult to read some freezemarks because of the color of the animal.

The following graph illustrates how to read a freezemark. If a mark is difficult to read, we recommend shaving the left side of the neck. You must know the freezemark of your wild horse or burro before you make an inquiry to a BLM office. 

Arizona 80001-160000	California 160001-240000
Colorado 240001-320000	Idaho 320001-400000
Montana 400001-480000	Nevada 480001-640000
New Mexico 640001-720000	Oregon 0-80000
Utah 720001-800000	Wyoming 800001-880000
Eastern States 880001-880100

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