If a fee imposed under this chapter for deposit into the animal agriculture compliance fund is delinquent, the department may charge interest on any amount of the fee that is delinquent. The rate of interest shall not be more than the current rate published in the Iowa administrative bulletin by the department of revenue pursuant to section 421.7. The interest amount shall be computed from the date that the fee is delinquent, unless the department designates a later date. The interest amount shall accrue for each month in which a delinquency is calculated as provided in section 421.7, and counting each fraction of a month as an entire month. The interest amount shall become part of the amount of the fee due.