California Mastitis Test (CMT)

California Mastitis Test.

The California Mastitis Test (CMT) is a rapid, accurate, cow-side test to help determine somatic cell counts (SCC) in a specific cow. The test was developed to sample individual quarters to determine the presence of subclinical mastitis. A cow with subclinical mastitis does not have abnormal looking milk or other clinical signs such as a swollen or painful udder. The test can also be conducted on bucket and bulk tank milk samples to help determine somatic cell counts (SCC) of the entire herd.

How to Perform the Test: (See figures 1-5.) A small sample of milk (approximately teaspoon) from each quarter is collected into a plastic paddle that has 4 shallow cups marked A, B, C and D. An equal amount of CMT reagent is added to the milk. The paddle is rotated to mix the contents. In approximately 10 seconds, read the score while continuing to rotate the paddle. Because the reaction disappears within 20 seconds, the test must be read quickly.

Figure 1 Figure 2
Clean each teat with alcohol. Squirt a small amount of milk from each quarter into the appropriate quadrant of the paddle.


Figure 3 Figure 4
1/2 teaspoon of milk is sufficient. Mix an equal ratio of reagent to milk.


Figure 5
Read and record the results.

How to Read the Results: The CMT reagent reacts with the white blood cells and the mixture thickens or gels in proportion to the amount of infection present. To become accurate and consistent, practice this test on cows with a known SCC.

CMT Score    Average Somatic Count 
(Cells per milliliter)   
Description of reaction 
N (negative)    100,000    No thickening, homogeneous.
T (trace)    300,000    Slight thickening. Reaction disappears in 10 seconds.
1    900,000    Distinct thickening, no gel formation.
2    2,700,000    Thickens immediately, begins to gel, levels in the bottom of cup.
3    8,100,000    Gel is formed, surface elevates, with a central peak above the mass.

Treatment: Refer to the mastitis information found on page F500.