California Mastitis Test (CMT)

Introduction: The California Mastitis Test (CMT) is a rapid, accurate, animal-side test to help determine somatic cell counts (SCC). The term somatic cell is used to identify any cell in the body. With the CMT test, the somatic cells that are being measured are mainly neutrophils. Neutrophils are white blood cells that help the body fight infection and are present in increased numbers in the udder when the animal has mastitis. The CMT test was developed to sample individual udder halves to determine the presence of subclinical mastitis. The test can also be conducted on bucket and bulk tank milk samples to help determine somatic cell counts (SCC) of the entire herd.


California Mastitis Test.

How to Perform the Test: A small sample of milk (approximately teaspoon) from each teat is collected into separate compartments of a plastic paddle that has 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, the score should be read, while continuing to rotate the paddle. Because the reaction disappears within 20 seconds, the test must be read quickly.


Clean each teat with alcohol. Squirt a small amount of milk from each teat into the appropriate section of the paddle. 1/2 teaspoon of milk is sufficient.



Mix an equal ratio of reagent to milk. The paddle is rotated to mix the contents.



In approximately 10 seconds, read the score while continuing to rotate the paddle. This goat has a negative CMT score.

How to Read the Results: The CMT reagent reacts with the neutrophils, and the mixture thickens or gels in proportion to the amount of cells that are present. High levels of neutrophils indicate infection. To become accurate and consistent, practice this test on animals with a known SCC.

CMT Score   

Average Somatic Count (Cells per milliliter)   

Description of reaction

N (negative)   


No thickening, homogeneous.

T (trace)   

up to 640,000   

Slight thickening. Reaction disappears in 10 seconds.



Distinct thickening, no gel formation.



Thickens immediately, begins to gel, levels in the bottom of cup.



Gel is formed, surface elevates, with a central peak above the mass

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