The Microscopic Examination of Milk

The microscope has been used to observe and count bacteria and somatic cells in raw milk since the early 1900’s. It has proven to be a valuable tool to the dairy industry. The milk smear procedure in use today is outlined in detail in the most recent edition of Standard Methods for the Examination of Dairy Products (i.e., SMEDP, 17 ed) and other references. For somatic cell counting, the Direct Microscopic Somatic Cell Count (DMSCC) is considered an official reference method used for regulatory purposes for direct milk counts and/or for calibration of approved electronic instruments. The regulatory procedure for somatic cells is outlined in detail in the most recent FDA 2400 Form. With the exception of the type of cells counted, the 2400 form procedure can be used for bacteria as well. While the Direct Microscopic Clump Count (DMCC) for bacteria is not considered an official test for bacteria counts, it is used throughout the dairy industry to estimate bacteria colony forming units (i.e., “clumps”) in raw milk samples taken from the farm, the tank truck or the plant storage facility. The DMCC is most widely used to screen incoming raw milk supplies (i.e., tank-trucks) to determine whether the milk has an acceptable or legal bacterial load and has become accepted in some states as a legal method for rejection of unacceptable milk.