Idaho Code § 25-1141
Brands shall be made by hot iron or freeze iron and shall be done in such manner to be clear and recognizable, and legible so as to enable ready identification. The major character or characters on the branding iron when applied to cattle shall be not less than three and one-half (3 1/2) inches in height, and/or three and one-half (3 1/2) inches in length, width or diameter. The major character or characters on the branding iron when applied to horses, mules and asses shall be not less than two (2) inches in height, and/or two (2) inches in length, width or diameter. Brands made in any other manner or size not permitted by this section shall be invalid and will not be recorded. All brands presently recorded at the effective date of this act shall be valid brands, but provided further that upon renewal of such brands, then and in that event such brands must comply with this chapter. Brands for sheep shall not be subject to the height, length, width or diameter limitations imposed by this section, but shall be of such height, length, width or diameter as prescribed by the state brand board, and brands for sheep shall not be subject to the hot iron or freeze iron limitations imposed by this section for cattle, horses, mules and asses.
Idaho Code § 25-1141