California milk test - CMT

The California Mastitis Test (CMT, also known as the California Milk Test) is a simple indicator of the Somatic Cell Count (SCC) of milk. It works by using a reagent which disrupts the cell membrane of somatic cells present in the milk sample; the DNA in those cells to reacting with the test reagent. It is a simple but very useful technique for detecting subclinical mastitis on-farm, providing an immediate result and can be used by any member of farm staff. It is not a replacement for individual laboratory cell count sampling, but has several important uses.

A four-well plastic paddle is used, one well being used for each quarter of the cow to be tested. The foremilk is discarded, and then a little milk drawn into each well. An equal volume of test reagent is added and then the sample is gently agitated.

The reaction is scored on a scale of 0 (the mixture remaining unchanged) to 3 (an almost-solid gel forming), with a score of 2 or 3 being considered a positive result. This result is not a numerical result but is an indication as to whether the cell count is high or low; the CMT will only show changes in cell counts above 300,000.

The advantage of the CMT over individual cow cell count results is that it assesses the level of infection of individual quarters rather than providing an overall udder result, enabling the problem quarter(s) to be identified. It also provides a 'real-time' result; laboratory testing provides a historical result as it can take days for lab results to be returned.

A special reagent for the test is sold as 'CMT-Test', but domestic detergents ('washing-up liquid') can generally be substituted, being cheaper and more readily-available.