Wis. Stat. § 95.67

No person may use chemical, biological or disease control products in the treatment or care of food producing animals without substantially complying with instructions, warnings and directions for use on the product label. No animal or food product including milk of the animal shall be marketed for processing or use as food prior to the time specified on the label of a product used in the treatment or care of the animal. This section applies neither to licensed veterinarians who prescribe or administer drugs in conformity with federal restrictions nor to persons using drugs in a manner prescribed by a licensed veterinarian. This section shall not prevent a farmer from administering animal disease control products to livestock in compliance with instructions on the product label.