CellCheck is the new AHI-led national udder health initiative, which is focussed on building awareness, delivering best practice, setting standards and building capacity. Agreed clear, consistent messages and guidelines are essential to encourage change and enable progress. AHI has convened a technical working group whose role is to collate Irish and international expertise and research in mastitis control. This will produce an independent source of evidence-based science and practice, accessible to all. This article is based on the outputs from the AHI technical working group and Countdown Downunder technical materials.

What exactly is a CMT?
The California Mastitis Test (CMT) is a quick and easy ‘cow-side’ test that is useful in detecting subclinical mastitis by estimating the somatic cell count (SCC) of the milk. It can be carried out during milking, and gives instant results at a quarter level. The CMT kit consists of a plastic paddle with four separate wells, and a bottle of reagent.

How does it work?
A milk sample is taken from a quarter and is mixed with the reagent. When mixed with milk, the reagent causes somatic cells in the milk to rupture. When the DNA is released from these cells, it coagulates and so the mixture has a slimy appearance. The more cells that are present in the milk sample, the more ‘jelly-like’ the result.

When should I use it?
The CMT can be used to detect subclinical infections in cows before introducing them to the milking herd e.g. cows at the end of the colostrum period, or newly purchased cows. It can also be carried out on cows that have a high SCC milk recording result, to identify the infected quarters. Avoid using it in the first four days after calving, as the presence of colostrum will make interpretation of the results difficult.

How do I do it?    
Using the CMT is as easy as 1,2,3!
1.    After discarding the first 3-4 squirts of foremilk, collect 2-3 squirts of milk from each quarter in each separate well. Holding the paddle almost vertical, allow excess milk to pour out just until the line becomes visible. This is the correct amount of milk to have in the well.
2.    Add an equal amount of reagent to each well. Start swirling the paddle gently. Clockwise, or anti-clockwise, it really doesn’t matter! Continue mixing for 10 seconds.
3.    Look at the consistency of the fluid in each well (not the colour), and record the amount of gel reaction within 20 seconds (from none to almost solidified). Visible reaction disintegrates after about 20 seconds. Discard the mixture, and rinse out the paddle.
What do the results mean?
While the CMT does not give a numerical result it is a good indicator of infected quarters. The results from the CMT are generally categorised into one of five scores: negative, trace, 1, 2, 3. Interpretation is subjective i.e. what you score as 1, others might score as a 2. The important thing to remember is that any positive reaction (trace, 1,2 or 3) will indicate a high SCC in that quarter. To become accurate and consistent, practice the test on cows with a known high SCC.
The relationship between SCC values and CMT is not precise because of the high degree of variability in SCC values of each CMT score (Table 1).
Do diseases other than mastitis affect CMT readings?
No! SCC levels in milk do not relate to conditions elsewhere in the cow’s body such as uterine infections, lameness, stress or inclement weather. It is possible that an existing quarter SCC may increase if stressors are added.  

Where can I get a kit from?
CMT kits are available from reputable veterinary wholesalers and are very inexpensive. Replacement bottles of reagent can be purchased separately. This is one of the best investments farmers can make in their dairy - so encourage your clients to get one and start practising!