KBR Wild Horse and Burro Information Sheet


Since April of 1978, all mustangs and burros rounded up by BLM and the U.S. Forest Service have been identified with a unique, painless freeze-mark. The mark is put on the left side of the neck and is a series of right angles and straight lines that can't be destroyed or changed.

The freeze-mark was developed by Dr. Keith Farrell of Pullman, Washington, and was first used in Sweden around 1966. Aside from being painless and indestructible, it is readily visible, inexpensive, and easy to apply using one of two irons. A small iron is used to freeze-mark foals, and a larger one for adult mustangs and burros. The freeze-mark on the foals can increase in size by two-thirds when the foal is fully grown.

The iron is placed in liquid nitrogen until it reaches a cold minus-32O degrees Fahrenheit. The animal's hair is then clipped as close to the skin as possible using standard animal clippers. The area to be marked is thoroughly washed with alcohol, and the iron is held to the skin of dark horses for 10-20 seconds, and to the skin of light horses for 40-50 seconds. After 30-60 days, the hair on the dark colored horses will grow back white. On light colored animals, the hide turns dark.

Each state where mustangs and burros are located is assigned a series of numbers unique to the animals within that state. After an animal is freeze-marked, the number is recorded and maintained indefinitely in BLM's central computer data base in Denver, Colorado. The information is available in each of the BLM offices across the country through the computer terminal. Each freeze-mark is tied to about 100 categories of information in the computer data base, ranging from the capture area, to the adopter's address.

Dee Grieser from Cryo Kinetics emailed in the following additional information:

The horizontal line under the last six digits of a freeze mark acts as a control. IF there is any distortion of the mark due to anatomical changes in the horse, the symbols should be read according to the underline. A 6 could be easily mistaken for a 5 or a 7 if the horse has become cresty, gained weight, etc. Most people don't give that line a second thought but it is there for a good reason. Dr. Farrell thought of everything when he developed this system.

Thanks, Dee, for that important tidbit!

As the horse gets older
the freeze-mark tends to blur.
By clipping the horse, it often
again becomes legible.

This is Sierra, owned by
Diane Johnson.

Here is a general guideline in which you can tell what state or region a horse came from based on the horizontal characters in the freezemark:

Please note that some states actually perform gathers in adjacent states. For example, many horses from Nevada will have California numbers.

000000 to 080000 - Oregon
080001 to 160000 - Arizona
160001 to 240000 - California
240001 to 320000 - Colorado
320001 to 400000 - Idaho
400001 to 480000 - Montana
480001 to 640000 - Nevada
640001 to 720000 - New Mexico
720001 to 800000 - Utah
800001 to 880000 - Wyoming
880001 to 880100 - Eastern States

For a related feature, see Signalment Codes

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