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.
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.
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