Except as provided in this regulation, a person may administer a medically important antimicrobial drug to cattle, swine, or poultry if, in the professional judgment of a licensed veterinarian, the medically important antimicrobial drug is necessary: To treat a disease or infection; To control the spread of a disease or infection; or For a surgery or medical procedure. A person may administer a medically important antimicrobial drug to cattle, swine, or poultry if, in the professional judgment of a licensed veterinarian, the medically important antimicrobial drug is necessary for prophylaxis to address an elevated risk of contraction of a particular disease or infection. Unless administration of a medically important antimicrobial drug is consistent with §A of this regulation, a person may not administer a medically important antimicrobial drug in a regular pattern to cattle, swine, or poultry. A person may not administer a medically important antimicrobial drug to cattle, swine, or poultry solely for the purpose of: Promoting weight gain; or Improving feed efficiency. Dry Cow Treatment. General Rule Requiring Assessment. The administration of a medically important antimicrobial drug to a cow entering a dry cycle is prohibited except when the cow is diagnosed with a bacterial intramammary infection (mastitis). Methods of Assessing Mastitis in an Individual Cow. Tests. A person may assess the presence of mastitis in an individual cow through one or more of the following tests: A positive bacterial culture test; A positive California Mastitis Test; A somatic cell count for an individual cow greater than 200,000 cells per milliliter in the most recent lactation; and Any other assessment method approved by the Secretary generally recognized by the American Association of Bovine Practitioners. Signs of Mastitis. A person may assess the presence of mastitis in an individual cow using one or more of the following indicators: Visibly abnormal milk including the presence of clots, blood, or discoloration; or Heat, pain, tenderness, or swelling of a gland. A licensed veterinarian may assess the presence of mastitis in an individual cow through the observation of clinical signs of mastitis.