Iowa Code § 579A.3: Enforcement.

While the cattle are located at the custom cattle feedlot, the custom cattle feedlot operator may enforce a lien created in section 579A.2 in the manner provided for the enforcement of an agricultural lien as provided in chapter 554, article 9, part 6. After the cattle have left the custom cattle feedlot, the custom cattle feedlot operator may enforce the lien by commencing an action at law for the amount of the lien against either of the following:

1. The holder of the identifiable cash proceeds from the sale of the cattle.

2. The processor who has purchased the cattle within three days after the cattle have left the custom cattle feedlot.