Mont. Code § 81-4-214
Every person except an owner, and the owner only when branding on the owner's own premises and in the presence of two responsible citizens, who marks or brands any calf or cattle that are running at large between December 1 and May 10 of the next ensuing year and every person who shall at any time brand or cause to be branded or marked any horse, mule, cattle or head of cattle, sheep, llama, alpaca, bison, swine, or other animal, 1 year old or older, with any piece of metal or implement, other than a branding iron, which branding iron must be of the same design as the brand or mark owned by the party using it, or who marks or brands or causes to be marked or branded any of the animals listed in this section with any piece or pieces of iron called "running irons", such as bars, rings, half or quarter circles, is punishable by imprisonment in the county jail for not exceeding 6 months or by a fine of not less than $25 or more than $500, or both.
§ 81-4-214, MCA