Iowa Code § 166.38: Compensation.

No licensed veterinarian shall receive, directly or indirectly, any compensation of any kind for the handling, sale, or use of any biological products, other than the veterinarian’s charges for administering the same, unless the veterinarian makes known in writing the amount of such compensation, if requested to do so by the person using biological products. Any veterinarian violating this section shall be guilty of a simple misdemeanor.