Each milk plant engaged in processing milk shall, at least once in each calendar month, collect and submit to a milk laboratory, which has been certified by the commissioner under N.H. Rev. Stat. § 184:82-a, for analysis a sample of milk of each producer supplying milk to such milk plant. Such laboratory shall determine the bacterial count of such samples as raw milk, such determination to be made by the standard plate count method, as well as a determination for such harmful substances as the milk sanitation board may by regulations require and shall keep a record of such findings for a period of not less than one year following any such findings which shall be open to inspection by the commissioner. The laboratory shall make a report to the milk plant submitting any such samples, and said laboratory shall transmit a copy of each such report to the commissioner.