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The basics of on-farm culturing: How we’re identifying milk quality issues on our farm

Kelli Woodring for Progressive Dairy Published on 16 September 2019
Quad Plate

Have you ever noticed some strange mastitis on your farm? And when you treat it, it doesn't seem to improve? Or it just keeps coming back? This is most likely because you are treating it incorrectly.

This year we decided to identify what types of bacteria are causing mastitis in our cows and what the appropriate next steps are. After attending a milk-quality workshop, we decided to try on-farm culturing.



We needed a few supplies to get started, and the Penn State Extension office helped us out. They provided us with the quad plates, milk sample tubes and sterile swabs. We provided the incubator and the mastitis.

The first step is to collect a milk sample from an infected cow. We prep the cow, swab the teat end with alcohol, strip a few squirts of milk into a sterile tube, and refrigerate the sample until the end of milking. Then we label which cow and quarter it's from.

Next we open the quad plate. The quad plate is a culture plate divided into four chambers. The first chamber is bright red and is used as a growth control; most bacteria are capable of growing here. The second chamber is orange and is for the gram negatives. This is where the coliforms, E. coli and klebsiellas will grow. The third chamber is the yellow one and is specifically for staphylococci infections. And the final chamber is the brown/red one and is for streptococci infections.

With the open quad plate, we take the sterile swab and make a zigzag mark with the milk onto each chamber. We close up the plate, and place it in the incubator for 24 hours. Hopefully within that time the bacteria will begin to grow, and we are on our way to identifying the mastitis.

After 24 hours it is time to check the results. There are many sources online with pictures to help you translate exactly what you are looking at. Sometimes the chambers will have pink, black or white dots, which are bacterial colonies. Depending on what they look like and which chamber they grew in, you can determine what type of mastitis you are dealing with.


Once you determine what type of mastitis you are working with, then it is time to make some decisions. It is best to have a treatment plan setup with your veterinarian. That way you can easily point to which treatment to use for which type of mastitis. Or, if there is a better solution such as non-treatment or culling.

With the help of on-farm culturing, we are able to make informed treatment decisions instead of shooting in the dark blindly and hoping our treatment will cure the mastitis. This method saves us time and money and can get our cows feeling better quicker.  end mark

Editor's note: Progressive Dairy recommends dairy producers work closely with their herd veterinarian for culturing milk quality samples and for making treatment decisions.

PHOTO: The quad plate is a culture plate divided into four chambers. Each chamber has a different purpose for bacteria growth. Photo by Kelli Woodring. 

Kelli Woodring
  • Kelli Woodring

  • Dairy Producer
  • Shippensburg, Pennsylvania
  • Email Kelli Woodring