Milk Testing

One of the most useful & practical tests for those who own a dairy cow is milk testing!

  • Prevention is all about cow health from udder health to general cleanliness.
  • “Somatic cell” testing is a cheap, useful indicator of general udder health.
  • Bacterial cultures from individual quarter(s) can help identify specific pathogens.

– HOW – TO sample milk –

First, you need to find a lab nearby or one that offers the type of testing you need:

Second, you will need to call up that lab and ask them the pertinent following questions:

  • Do you offer somatic cell testing, and testing for butterfat and protein percentages? Price?
  • What kind of a container do I need to use for the samples? (Based on that answer, they may need to send you tubes, and make sure to get extra!! or you might be able to get them directly from your vet or a neighboring dairy farmer.)
  • Do you offer culturing or DNA testing for bacteria? Price?
  • If I ship the samples, how do they need to be packaged and what is the cost? Is there a DHIA tester in my area that I could give the samples to?

Third, taking the sample is the most important step!


Accuracy comes from proper clean handling:

1) Make sure everything is properly cleaned – your hands & the udder. Use alcohol swaps and thoroughly clean the teat ends.

2) Only use sterile tubes for collecting. Label each tube before collecting (FR, FL, RR, RL for front/rear and right/left quarter. Think of it as the cow’s left and right, the cow’s front and back.)
3) Taking samples from each quarter and use a separate tube for each quarter.  (If testing for fat and protein, one group sample is sufficient – and sanitation is not as critical as if testing for specific bacteria.)
4) Don’t take the first milk. Milk out each quarter a bit, then take a sample. (For fat and protein only, one group sample is sufficient and can be taken from your machine after milking is done.DSC06021
5) Freeze sample immediately, ship asap early in the week – overnight or next day (some labs work with preservatives, their handling procedure may be a bit different. Please read the online instructions or call the lab before sending in a sample for the first time.).

Fourth, reading the results:

  • SOMATIC CELL = Lower is better. The “score” will be 1,2,3,4,5, etc. and the “count” will be in thousands. So it may show up as 24 or 24,000 and they are the same thing. A “healthy” cow will have somatic cell below 200 (thousand). Ideal range is 0-150, 150-250 is acceptable, above 400 and you might seriously question the health of the animal. 750 is the legal limit for milk sold commercially. Anything in the millions indicates infection.
  • BUTTERFAT = If you want a cow that you can get lots of different products from (like skimming cream and such) you probably want the buttefat level to be above 4 percent. Butterfat CAN be changed through different feeding. For example, putting a cow out on fresh spring pasture tends to decrease butterfat % for a couple months while the grass is watery, fast growing, and plush. Generally, intense commercial diets encourage lower butterfat and more overall production. Most cows going to a family cow environment will lose production but gain butterfat by percentage. Butterfat depends somewhat on the breed, although within each breed is a lot of difference. I’ve seen Jerseys with 2.9% butterfat and Jerseys with 8.5% butterfat! Also, a fat cow does tend to give more butterfat, so if your cow is prone to stay thin or is unhealthy, their butterfat score will also be lower, typically. DSC06020
  • PROTEIN = Is not adjustable as much as butterfat via feed. Protein in almost any dairy cow will be between 3.0 and 4.2, you won’t see many cows outside that realm. Higher is always good, more “cheese yield”! Protein levels tend to be higher in “protein” breeds such as Jersey, Guernsey, or Swiss.
  • CULTURES = There are numerous bacteria that may be present on a culture. If something shows up, the lab should be able to indicate what the bacteria comes from. Most bacteria come primarily from either udder infection (Staph Aureus, etc.) or sanitation problems (E. coli, Klebsiella, etc.) so the identification of bacteria does a lot to explain the problem. You can take samples directly from the teat OR bulk samples from the tank of your machine or a jar in the fridge. I like to take samples from the fridge for maintenance because that is where you will be drinking the final product and any bacteria there may indicate that you need to adjust your sanitation practices. Even the most stringent sanitation measures may not be enough (for example, even the air hose from your machine to pump can harbor bacteria that infiltrates the milk!)



Below is a sample test result.

  • Negative = none counted.
  • Positive = bacteria identified. (Either infection or environmental contamination)
  • Multiple +++ indicates stronger infection.


FAQ: I asked the lab: “If the cow has been actively treated with antibiotics before the milk test is sent in, will the PCR be detecting live, dead, or both types of bacteria. Is there any way to tell the difference, or would a healing cow have a low number because the bacteria are dead?

API answered: “The mastitis PCR is looking for specific DNA that Identifies the bacteria and thus will find both live and dead bacteria.  There is now way to different live from dead using PCR.  Culture plates are the only way to quantify live bacteria.  As the cow is “healing” the bacteria is being controlled/removed from the body so to heal the bacteria have to be killed and or removed.

The control (below) is to make sure the lab did not have a contamination of the sample.



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