Let’s agree that not all mastitis infections are created equal. Some infections are more severe than others and actually make the cow sick, while others result in only a few flakes or clots in the milk that are difficult for technicians to detect.
Some mastitis pathogens have a high tendency to become chronic, predominantly because they reside in tissues deeper in the udder (Staph aureus) or because they are not susceptible to common intramammary antibiotics (Mycoplasma or Prototheca). Others will have no remaining viable bacteria left by the time we see clinical signs.
Why, then, would we treat all mastitis cases the same? Clearly, with this many differences, treating all the cases or treating none of the cases should never be the best answer.
In today’s world of antibiotics scrutiny, we should be trying to treat only the cases that can actually benefit from treatment. This means dairies should be taking a closer look at on-farm culture as a part of their milk quality programs.
The goal of culturing clinical mastitis cases on the dairy should not be to determine the exact species of bacteria causing the mastitis, but to group them into basic categories. The main categories are gram-positive, gram-negative, no-growth and, potentially, Streptococci with the use of tri-plates.
This tells us much of what we need to determine whether or not to treat a case and what duration of therapy is likely necessary to gain an acceptable cure rate.
Because you will be basing economic and biological decisions off of the results, all efforts need to be put into ensuring the quality of the process from start to finish. The key quality control points for on-farm culture are:
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It all starts with clean samples. No matter what mastitis diagnostic you choose, the results will only ever be as good as the cleanliness of the samples provided to the lab. Wash and sanitize gloves between every cow. If the cow has already been prepped, clean the teat and teat end with an alcohol swab.
I like to use baby wipes that are spiked with additional isopropyl alcohol, as they are easier to work with in the palm of my hand and are more conducive to cleaning the entire teat. Pay special attention to the teat end cleanliness before sampling.
Pop the vial lid only immediately before taking the sample. Hold the vial sideways (45- to 80-degree angle) to prevent debris and contamination from the udder falling into the sample. Turn the teat and squirt to the side or back into the sideways vial.
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Incubator temperature is critical. Temperature drift in incubators is one of the most frequent problems I see on dairies. I typically recommend all dairies have a digital thermometer in their incubators. Most drug companies have digital thermometers for dairy refrigerators where vaccines are stored.
Many of these have a range high enough to monitor an incubator and are also easy to read and have the distinct advantage of being free. I recommend that dairies chart the incubator temperature daily to ensure the temperature is always within a pre-defined window.
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Make sure stocks of plates and other materials are fresh and supplies are “turned” often. I frequently see dairies that have very old stocks of plates and materials. Smaller dairies often do not have enough cases to use plates fast enough.
Larger dairies are tempted to save pennies on bulk pricing deals and may overstock themselves. Plates, even stored in a refrigerator, can occasionally dry out over time or may even become contaminated by molds or other bacteria.
One way to counter this is to place a blank or unstreaked plate into the incubator on a routine basis. If the plate has any growth on it at 24 hours, the batch is contaminated.
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A culture program takes continuous training, oversight and monitoring. With excellent techniques and quality control, we typically expect between 30 and 40 percent of samples will have a no-growth result. No-growth samples tell us a lot about the culture process.
There are exceptions, such as bacteria that need special conditions to grow or poor incubator maintenance, but in general no-growth results tell us that we obtained clean samples and had excellent sterile plating techniques. The opposite condition is where multiple different “bugs” appear on the plate.
Unless we are sampling multiple quarters in the same vial, most of our samples should yield a pure growth with colonies that appear very similar visually. If there are three or more distinct colonies on the plate, then it needs to be read as “contaminated.”
Dairies need to monitor their culture distributions, especially their no-growth and contaminated results, and feed that information back through the dairies’ milk quality teams regularly to trigger retraining or reassessment of the process.
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No dairy can or should go it alone. Having sound lab techniques and obtaining consistently accurate results takes skilled and dedicated employees. That takes training, typically from or through a veterinarian.
Even with a strong training regimen, on-farm programs are not designed to give you all the answers you need to manage milk quality. Every dairy still needs some relationship with an outside culture lab.
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You still have to evaluate the cow herself. Looking at the cow’s clinical mastitis and SCC history before making a treatment decision is a necessary component of achieving the best long-term results for your program.
Cows with histories of repeated clinical cases or months of high SCC prior to the current mastitis case are less likely to cure no matter what the culture results.
Similarly, for cows that have systemic signs of illness, such as a significant fever, or that are off-feed, we should not be waiting on culture results to decide on treatment. Whether your protocol on these cows includes antibiotics or simply supportive therapy, the time to intervene is immediately, when the cow is found.
The dairy industry is under intense pressure to make more judicious and prudent decisions with antibiotics. On-farm culture, with sound management, can be a powerful tool to not only meet this need but to also gain greater understanding of the mastitis dynamics on your dairy. PD
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Brandon Treichler
- Quality Control Veterinarian
- Select Milk Producers
- Email Brandon Treichler
