Iowa Code § 351.28: Liability for damages.

The owner of a dog shall be liable to an injured party for all damages done by the dog, when the dog is caught in the action of worrying, maiming, or killing a domestic animal, or the dog is attacking or attempting to bite a person, except when the party damaged is doing an unlawful act, directly contributing to the injury. This section does not apply to damage done by a dog affected with hydrophobia unless the owner of the dog had reasonable grounds to know that the dog was afflicted with hydrophobia and by reasonable effort might have prevented the injury.