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Q: I got a no-growth result on a clinical mastitis diagnostic test?? What can this mean?

A: Getting a no-growth result from a clinical mastitis diagnostic test is pretty common. In fact, around 10-20% is around what is normal in clinical trials, and on many farms . Here are three possible explanations, the reasons behind them, and some tips on steps you might want to take.

1. It's just not bacterial:

Bovine mastitis is technically defined as inflammation of the udder. While the inflammation is usually caused by a bacterial infection, this is not always the case.

Possible non-bacterial causes could be a physical injury such as a knock to the udder, or a non-bacterial pathogen such as a yeast or a mould).

2. She's on the mend:

The cows immune system is pretty good at responding and eliminating some types of gram-negative coliform bacteria such as E.coli. It is possible you might have spotted the back end of an infection that the immune system has already cleared, and that the visible symptoms remaining are the residual effects.

Again, here it is unlikely that in this case an antibiotic would be effective, so your approach will most likely be observation until the symptoms go away. Some veterinarians may recommend pain relief or supportive care options.

3. It's technical:

Whatever method you use for culturing your samples, regular checking of equipment and processes is important to make sure your results are accurate.

If you're using manual plating and incubation methods, regular re-training and quality control measures are essential to ensure you are getting accurate results. You'll want to check your incubator and any other equipment working correctly, and have been calibrated if necessary.

If you use Mastatest, the cartridge system removes the chance of user-error that is there with plating systems. And importantly, our systems can detect an issue with your Lapbox, and we'll contact you to let you know via phone or email.

How do I manage a no-growth result?

Always follow the advice of your veterinarian.

Most veterinarians will recommend a watch-and-wait approach for mild-moderate clinical mastitis that reports as no-growth. Since the test indicates no active bacteria in the sample, antibiotics will probably not be helpful in managing the case. You might want to consider offering supportive therapies.

If you use Mastatest, your test result email will outline your vet's recommended management strategy

If symptoms don't improve, or the animals condition declines, then prompt re-testing and vet review are important. 

In Summary:

The most likely reason for you no-growth result, is that there is not any active bacterial infection due to a non-bacterial cause of inflammation, or the infection having already been cleared. Your vet will probably recommend a watch and wait strategy, with re-testing should the original symptoms not subside.