Iowa Code § 164.11: Identification mark.

A designated animal subjected to an official test shall be plainly and permanently marked for identification in a manner authorized by the department. Native grade bovine carrying the calfhood vaccination and calves vaccinated after importation from other states shall be tattooed in the ear. Officially vaccinated purebred registered cattle must receive a vaccination tattoo and either an official vaccination tag or a purebred identification tattoo. The vaccination tattoo and the vaccination tag number or the purebred identification tattoo shall be evidenced on the official certificate of vaccination.