My vet always talks about the Dairy Antibiogram. What is this and how can it be of use to me?

My vet always talks about the Dairy Antibiogram. What is this and how can it be of use to me?
By Jemma Guyton, Veterinarian, Anexa Vets Te Aroha

A Dairy Antibiogram (DAB) is a test which detects and monitors antibiotic resistance in mastitis bacteria on your farm. This allows for fine tuning and targeted use of antibiotics on your farm.

All you need to do is talk to your vet and ask them to request a test on your behalf. Your dairy company will be notified, and a sample will be taken from the bulk tank and sent to the lab for testing.

If present in your bulk milk, the two main mastitis-causing bugs Staph aureus and Strep uberis can be grown from the sample. These bugs are then incubated in increasing concentrations of different antibiotics. This then shows which antibiotics, at which concentration are effective. This information is collected in a report and sent to your veterinarian who will interpret it for you.

Even if you’ve had a DAB run before, it’s a good idea to do them every season to keep track of the changes of resistance in your mastitis bugs, especially if you are buying cows. For example...

One of our Morrinsville clients had their first DAB test run this Spring. Results showed that penicillin would be very effective against Strep uberis but extremely penicillin resistant Staph aureus was isolated. This meant neither intramammary nor injectable penicillins could be used. This was tricky as the farm preferred penicillin-based mastitis treatments and didn’t want to change products.

At the DAB report discussion, the veterinarian explained the results and therefore how important milk cultures would be. The farmer was immediately able to understand - if the bug was Staph aureus treating WITHOUT culture would mean:
  • wasting time and money trying to cure
  • exposing the bugs to penicillin that would further select for penicillin resistant Staph aureus.


However, if culture grew Staph aureus, he would have been able to decide how to manage her and not spend the money trying to treat her with lactating cow products. On the flip side, if Strep uberis was grown, penicillin would be a great option. Research has shown that delaying treatment for 24 hours until the interim result is reported does not affect cure rate. In the meantime, the cow should be drafted out of the milking herd and given a dose of anti-inflammatories to help with pain and inflammation.

This case study shows how valuable a DAB can be. It allowed this farmer to realise that he had an antibiotic resistance issue. He then decided to use tools such as milk sampling to focus his antibiotic usage to give him the best results.

The example is not unusual, 30% of farms sampled have Staph aureus resistant to penicillin and 40% of farms sampled have Strep uberis that are difficult to kill with cloxacillin. Where does your farm sit in this space? Are you getting the best results to the antibiotics you are using? Ask your vet at your Milk Quality Consult.



Date Added: Friday, 7th February 2020


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