Iowa Code § 169C.2: Custody.

A landowner may take custody of livestock if the livestock trespasses upon the landowner’s land or strays from the livestock owner’s control on a public road which adjoins the landowner’s land. A local authority may take custody of the livestock as provided by the local authority. The landowner shall not transfer custody of the livestock to a person other than the livestock owner or a local authority, unless the livestock owner approves of the transfer. A local authority shall not transfer custody of the livestock to a person other than the livestock owner or a livestock care provider.