331.304A  Limitations on county legislation.
  1.  As used in this section:
  a.  “Aerobic structure”, “animal”, “animal feeding operation”, “animal feeding operation structure”, and “manure” mean the same as defined in section 459.102.
  b.  “County legislation” means any ordinance, motion, resolution, or amendment adopted by a county pursuant to section 331.302.
  2.  A county shall not adopt or enforce county legislation regulating a condition or activity occurring on land used for the production, care, feeding, or housing of animals unless the regulation of the production, care, feeding, or housing of animals is expressly authorized by state law. County legislation adopted in violation of this section is void and unenforceable and any enforcement activity conducted in violation of this section is void. A condition or activity occurring on land used for the production, care, feeding, or housing of animals includes but is not limited to the construction, operation, or management of an animal feeding operation, an animal feeding operation structure, or aerobic structure, and to the storage, handling, or application of manure or egg washwater.
98 Acts, ch 1209, §9, 53