Mont. Code § 81-4-508
A person claiming to be the owner of an abandoned horse or horses may serve written notice upon the roundup supervisor in charge of the roundup of the claim of ownership at any time before sale or other final disposition of the horse or horses. The claim of ownership must be verified by the oath of the claimant or someone on the claimant's behalf, and the sale or other final disposition of the horse or horses must be postponed from time to time as may be necessary to enable the claimant to make proof of the claim as provided in 81-4-509. The postponement may not be allowed unless the claimant pays to the roundup supervisor in charge of the roundup or delivers to the supervisor satisfactory security for the estimated cost of keeping and feeding the horse or horses until sale or other final disposition or delivery to the owner.
§ 81-4-508, MCA