Strep ag is a highly specialised bacteria that causes mastitis in cows, elevating cell counts in infected quarters. It is also highly contagious, so if infection is unchecked, many cows in the herd will become infected leading to an increase in Bulk Milk Cell Counts.

In a recent study of vat milk from 42 farms in Victoria, Strep ag was found in 60% of the herds with BMCCs above 400,000 cells/mL.

It isn’t possible to tell which bacteria are responsible for infections by looking at milk, udders or cell counts. At present, the only way to know for sure whether Strep ag is the cause of the problem is to get the lab to grow the bugs by milk culture and analyse the culture.

When planning an investigation of a herd cell count problem, it’s important to consider the number of samples required to find the culprit bacteria, the type of samples to take (for example, whether “composite” or quarter samples will give the best information) and which cows to target.

Collection and transport techniques are also important and the testing lab must have the ability to differentiate Strep ag from the other strep bacteria that can infect udders.

If you suspect that you have a problem because your Bulk Milk Cell Counts are rising, or are consistently over 250,000 cells/mL, talk to one of the professionals who advises you on milk quality and they will either recommend a plan or refer you to a colleague who can help.

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Milk sampling is essential to confirm the presence of Strep ag in your herd.

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Guideline 10, Fact Sheet A