Some years ago, Streptococcus agalactiae (Strep ag) was a relatively widespread cause of mastitis in the Australian dairy industry.

It was then commonly known as “Contagious Mastitis”, due to its ability to spread rapidly in a herd.

Because cure rates for treatment of Strep ag are remarkably high, the widespread uptake of antibiotic dry cow therapy into a seasonal milking system nearly eradicated Strep ag from many regions of Australia.

However the trend towards both split and year-round calving, combined with widespread movement of cattle as herds have been sold and disseminated, has seen Strep ag begin to re-appear as a significant cause of mastitis in Australia.

In fact, we are always dealing with a number of Strep ag herds, and it seems that as soon as we have dealt with one herd, another one pops up – Strep ag is not going away any time soon!

Diagnosis of Strep ag in a herd is easily done with either milk cultures and/or the new PCR tests that are now available.

A key feature of Strep ag is that it only spreads in the dairy during milking, so the milking process, milking machines and most especially post-milking teat disinfection (teat spraying/dipping) are critical to both control and eradication of this bug.

Strep ag only spreads in the dairy during milking.

Because of the rapid spread, herds with Strep ag will often see both high and very variable Bulk Milk Cell Counts and Individual Cow Cell Counts (which can often be in the millions without actually being a clinical case).

Despite being a highly contagious cause of mastitis, it is one of the few mastitis bacteria that can be completely eradicated from a herd, and it will not return unless infected cows are introduced into the herd.

Strep ag is so contagious that it is unlikely to just “disappear” on a farm; it will always need an eradication strategy.

The good news is that a well designed Strep ag eradication plan is generally highly successful at removing it from the herd - the bad news is that these plans can sometimes be both costly and complex!

It is also important to remember that Strep ag is not going to be the only mastitis bug on a farm, so an overall strategy that deals with all mastitis risks will still be needed.

Fortunately, everything that is done as part of a Strep ag eradication program is also highly relevant to other causes of mastitis.

Every herd owner/manager should think about how they will make sure that Strep ag doesn't get into the herd; the answer is simple for most herds!

You can keep Strep ag out by simply adopting a policy of never buying cows without an appropriate PCR test strategy on milk from either the cows being purchased or from the vat of the herd of origin.

Testing is simple, quick and relatively cheap. In most cases it can be easily organised - contact your factory field officer, your vet, or call us here at Dairy Focus.

You can keep Strep ag out by never buying cows without an appropriate PCR test strategy.

Keep your risk of getting Strep ag as low as posssible - there should be no reason for a herd to let Strep ag in!

Key points to remember with Strep ag:

  • Strep ag is highly contagious but it only spreads in the dairy during milking.
  • Although Strep ag responds very well to treatment, an eradication plan will be necessary to remove it from a herd.
  • A simple PCR test on bulk milk will tell you whether you have Strep ag in your herd or not.
  • You can avoid “buying-in” Strep ag by PCR testing the milk of cows you intend to purchase.
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