Strict liability since the 1870s
Under Iowa Code §351.28, an owner is liable for all damages when their dog attacks or attempts to bite a person, or worries, maims, or kills a domestic animal — regardless of the dog's prior history. The rule traces back to the Iowa Code of 1873, making it one of the longest-standing strict liability dog bite statutes in the country.
The statute's only real exception applies when the injured party was doing an unlawful act that directly contributed to the injury — narrower and more specific than a general "provocation" defense, and focused on the victim's own illegal conduct rather than whether they provoked the dog. A separate carve-out applies to rabid dogs: that damage falls outside strict liability unless the owner had reasonable grounds to know the dog had rabies and could have prevented the injury through reasonable effort.