News & Advice

Mastitis is bugging farmers this season, but which bugs are to blame?

Feb 7, 2023 | Dairy, Milk Quality

Katrina Roberts, Herd Health Veterinarian

It has definitely been a challenging season for mastitis, and it is easy to blame the weather. Without knowing which bacteria are causing the mastitis issues in your herd (clinical or subclinical), we cannot just assume that the weather is the problem.


If you answer ‘yes’ to any of these questions, then you need to read on…..

  • Are you frustrated that the antibiotics you are using aren’t clearing the clinical cases?
  • Is your Bulk Tank Somatic Cell Count (BTSCC) over 250k but you can’t find anything on the filter sock?
  • Are you still getting clinical cases every week even though it’s late lactation?
  • Have you enviously watched the neighbours go OAD, but know you can’t because your BTSCC is too unpredictable? 


Which bugs are causing mastitis problems this season

The results from our Anexa lab (as well as veterinary labs throughout New Zealand) show the majority of milk samples contain the environmental bug, Strep uberis. We often see more Staph aureus (contagious bacteria which spread from cow to cow) appearing later in lactation, but this is not the case in all herds.

Unfortunately, we can’t tell which bug is causing mastitis by how the mastitis ‘looks’. The clinical signs we see are due to the cow’s immune system’s response to the bug as well as the bug’s unique characteristics, meaning the same family of bug can cause different clinical signs in different cows!

This season is one out of the box and no one wants to be culling cows at the moment. This means that there are ‘problem cows’ still being milked on many farms that would ordinarily be gone by now. From a mastitis perspective, you have to decide which cows to cull and which cows can stay to make some cheap milk for you on grass until the last day of the season! Repeat high somatic cell count (SCC) cows, staph aureus infected cows, cows with poor udder conformation, 3 titters and slow milkers… Who should stay and who should go?!


How do I know which mastitis bugs are causing issues on my farm?

Knowing what kinds of bugs are causing mastitis in YOUR cows is crucial to making treatment recommendations and prioritising areas for improvement. Along with doing a Dairy Antibiogram (bulk milk mastitis resistance profile; see our previous Dairy Antibiogramarticle for more information), taking milk samples for culture is a great way to help understand the mastitis issues in your herd.

Milk cultures help to identify bacteria that cause mastitis in individual cows, meaning you can tailor treatments for these animals. But more importantly, at the herd-level, milk cultures can help build a picture of what types of bugs (contagious or environmental) are most prevalent in your herd at specific times of the year. The more cultures you have, the easier it is to see a pattern i.e. Are you growing a lot of strep uberis? This is an environmental or ‘mud bug’ – are there muddy gateways that cause issues in winter, spring and this season in summer as well!?


How many milk samples should be collected?

We recommend a minimum of 10 samples to get started (Review our guide: How to collect a milk sample). Collect sterile milk samples from cows that had a high SCC at a recent herd test, as well as always collecting sterile pre-treatment milk samples from every clinical case throughout the season. You can freeze samples and submit them at your convenience to your local Anexa vet clinic.

Take advantage of our 10+ milk sample deal when you submit 10 or more milk samples to your local Anexa clinic for culture at our Anexa Morrinsville Lab and get 10% off (if you don’t require individual cow results urgently).


Case Study

Recently a herd with an average cell count below 80,000 spiked up to 160,000 with an increase in clinical cases. Samples were taken from six cows with clinical mastitis (before being treated). Results returned a mixed bag of bugs including a couple of coagulase negative staph (CNS). Because there were only six samples and there was a mixture of bugs cultured it was difficult to make clear recommendations at herd-level for the farmer. We did however, request that the farmer collect more samples. A further 15 samples were submitted 10 days later.

From this larger group of cultures, it was easier to see a pattern in the types of bugs grown – predominantly contagious bugs, mainly CNS. It was determined with the growth of CNS that teat spraying was not up to scratch. CNS doesn’t often cause clinical mastitis, (it does push up BTSCC, as in this herd), however it is a good indicator of how effective teat spraying is on farm, as CNS (which grows at the teat end) is easily killed with all teat spray active ingredients. After more investigating of this farm’s teat spray (product, preparation, storage, application and technique), the veterinarian determined that technique was great, but the type of teat spray was not suited to the farm. Since the change of teat spray clinical mastitis rate and SCC has decreased dramatically.

More samples builds a better picture, without the milk culture results we are flying blind!


Planning for next season

If we have enough milk culture results from your herd and a current Dairy Antibiogram (DAB), when we meet for you milk quality consult we can provide you with the best advice possible to lower your SCC and reduce your clinical mastitis case rate.  If you haven’t done a DAB on your herd this season (or are not sure if one is booked), please talk to your local vet now so they can get it booked now to have the results in time for your milk quality consult.

If you are interested in sampling a batch of cows, but feel that you don’t have the experience, staff or time to make it happen, give us a call or contact us through our website and we can arrange for Anexa staff to collect the milk samples for you, freeing you up to get other work done and giving you peace of mind that the samples collected will be suitable for culture in the lab.




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