Iowa Code § 619.7: Mitigating facts.

In any action brought to recover damages for an injury to person, character, or property, the defendant may set forth, in a distinct division of the defendant’s answer, any facts, of which evidence is legally admissible, to mitigate or otherwise reduce the damages, whether a complete defense or justification be pleaded or not, and the defendant may give in evidence the mitigating circumstances, whether the defendant proves the defense or justification or not.