Wis. Stat. § 173.09: Investigations.

In the course of investigation of suspected violations of statutes or ordinances, a humane officer may enter any building, vehicle, or place where animals may be present for the purpose of inspection, examination of animals, or the gathering of evidence. If the building, vehicle, or place to be entered is not public, and consent of the owner or person in charge is not obtained, entry shall be under authority of a special inspection warrant issued under s. 66.0119 or a search warrant.