California Mastitis Test (CMT) is a Good Tool!

The CMT was developed in the late 1950's at the University of California when it was discovered that certain types of detergents, when added to milk, caused gelling that correlated with higher Somatic Cell Counts (SCCs).

How it works and what does it measure?

Mixed with milk, the CMT solution reacts with the DNA of somatic cells. Somatic cells are mostly made up of white blood cells, also known as leucocytes. The more white blood cells that are present, the more pronounced the gelling. If a goat has an udder infection, the body will send white blood cells to the udder in order to fight off the infection. The milk and CMT solution will gel in proportion to the number of white blood cells present, indicating the severity of the inflammation.

CMT kit

Figure 1: CMT kit

Can CMT help solve a Bactoscan problem?

The CMT is a good tool to monitor SCCs. However, many producers have noted that the CMT can be useful in troubleshooting Bactoscan problems as well. A goat with subclinical mastitis does not have the typical swollen, painful udder or abnormal milk and can therefore go undetected as a source of infection. Occasionally, such goats with subclinical mastitis can shed bacteria in huge numbers causing the bulk tank Bactoscan test to spike. In these cases the CMT can be used to help identify a goat shedding high numbers of somatic cells and also contributing to a high bulk tank Bactoscan test.

Using the CMT

Under normal circumstances, teats are stripped before using the foremilk to conduct the CMT. Each half of the udder, or a composite of the two, can be tested. To do so, a producer needs to put about 2 to 4 mL of milk into a well on the CMT paddle. He then tips the paddle almost vertically, allowing the excess milk to drain out, leaving about 2 mL of milk in each well. Using the squeeze bottle, the producer adds 2 mL of CMT reagent and swirls the paddle in a horizontal motion. There will be a reaction depending on the number of somatic cells present in the milk. The biggest error performed during this test is the addition of too much milk and reagent to the wells, skewing the results, and making the gelling difficult to observe.

Interpretation of the CMT

CMT scoring is very subjective, in that each person performing the test may interpret the results differently. This is the biggest disadvantage of the CMT. Producers should begin by getting a clear understanding of what a negative and positive CMT result looks like (refer to table 1 below).

The CMT can be done on fresh goats; however, the milk of fresh goats may gel more even in the absence of significant subclinical mastitis. The milk of goats in very late lactation may react similarly. Therefore CMT results on fresh and late lactation goats are not always reliable.

Advantages and Disadvantages

There are a number of advantages regarding the CMT. Namely, it is fairly accurate in measuring somatic cells in individual goats. The test is also relatively inexpensive, and it is simple and easy to use. Unfortunately, the scoring and interpretation of the results may vary between testers, and the exact somatic cell count number is not achieved. Keep in mind that the results from fresh and late lactation goats may be doubtful.

Table 1: Interpretation of CMT visible reactions to estimate SCC
Description of visible reaction
(Cow SCC)
Mixture remains liquid and smooth. Perfectly clear reflection in fluid on bottom of paddle. 0-200,000 cells/ ml.
A light slime forms and is seen most easily by tipping the paddle back and forth and ob- serving the mixture as it flows over the bottom of the cup. There is a distorted reflection in the bottom of paddle. Trace reaction tends to disappear quickly with continued move- ment of the fluid.
Numerous distinct clumps appear but with no tendency toward a single gel mass. With some milk, the reaction is reversible and may disappear with continued movement of the paddle.
400,000-1,500,000 cells/ml.
The mixture thickens immediately with gel formation. As the mixture is swirled, it tends to move as a mass around the periphery of the cup forming a tail. When you tip the paddle, you can break the stream of liquid as it pours over the edge.
800,000-5,000,000 cells/ml.
A gel is formed which causes the surface of the mixture to become convex. An egg like appearance. This central peak may adhere to the bottom of the cup. When you tip the paddle, you cannot break the stream of liquid as it pours over the edge of the cup; it all comes out as one mass.
Cell number greatly over 5,000,000/ml.

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