California Mastitis Test (CMT)

What is the California Mastitis Test?

The California Mastitis Test is a simple quick test for the cell count of individual udder quarters. It is also called the Schalm test and is usually shortened to CMT. All you need is a test paddle with four cups and a test fluid. You see the result straight away in the barn.

The test fluid contains a detergent that breaks open the body cells in the milk. The genetic material released from the cells forms a gel. The more cells, the thicker the mixture. So the test does not measure bacteria, but the defence reaction of the udder.

When is a CMT useful?

• A cow’s cell count in milk recording has gone up and you want to know which quarter is affected.
• The milking robot reports rising conductivity.
• Before a bacteriological test, so that you sample the right quarter.
• Before drying off, to decide which cow needs a dry cow tube.
• In fresh cows, after the first days of colostrum.
• Without milk recording, as a herd check: testing all cows at one milking takes about an hour.

How to carry out the test

• Strip the first squirts from each quarter and discard them.
• Hold the paddle so that each cup matches one quarter, and milk about 2 ml into it. Most paddles have a mark.
• Tip off excess milk until the amount is right.
• Add the same amount of test fluid.
• Swirl the paddle in a circle for about ten seconds.
• Read the result immediately. After a longer time the gel changes.

Reading the result

• Negative: the mixture stays liquid. The quarter is healthy.
• Trace: slight streaks that disappear when you swirl.
• Single positive (+): clear streaks, but no solid mass yet.
• Double positive (++): the mixture thickens at once and pulls towards the centre.
• Triple positive (+++): a firm, jelly-like mass forms that you can lift almost completely out of the cup.

Compare the four quarters. One clearly positive quarter next to otherwise negative ones shows you where to start. If all quarters are slightly positive, this can also be due to the stage of lactation, because shortly after calving and at the end of lactation the cell count is naturally higher.

What the CMT cannot do

The test does not show an exact cell count or the pathogen. For a treatment decision or with recurring problems you need a bacteriological test.

Tips for reliable results

Always test before milking, not after, because the cell count is higher in the strippings. Rinse the paddle with water after each cow. Store the test fluid in a cool, dark place and check the use-by date, as old fluid reacts more weakly. Write down the result per quarter so that you can compare it after two weeks.

Frequently asked questions

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