Using Freeze Marks
The BLM uses freeze marking to identify wild horses and burros that have been gathered from the public rangelands because of overpopulation. Freeze marking is a permanent, unalterable, and painless way to identify each horse. The mark 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 symbols are applied with an iron chilled in liquid nitrogen. The hair at the site of the mark will grow back white and show the identification number.
Mares that have received fertility control vaccines are usually freeze marked with an identifying brand on their left croup, although some have identifying freeze marks on their necks.
In addition to the freeze mark that all horses and burros removed from the range receive 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 freeze mark on the neck.
Although every effort is made to apply freeze marks 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 freeze marks because of the color of the animal.
The following graph illustrates how to read a freeze mark. If a mark is difficult to read, we recommend shaving the left side of the neck. You must know the freeze mark of your wild horse or burro before you make an inquiry to a BLM office.