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Recently we have seen a few cases of cows with toxic mastitis. In this scenario, cows with mastitis become very sick, very quickly and are often unable to stand. They need to be treated with antibiotics, anti-inflammatories, electrolytes and fluids. Even with this supportive care they can sometimes die.

We find two bacteria associated with toxic mastitis more than any other: E. coli and Staph aureus.

Sneaky Staph aureus

Staph aureus is a cow-associated bacteria: found in the milk and on the teat skin of infected cows. It generally spreads at milking time. For example, from teat to teat on contaminated milker’s gloves or when post milking teat spray coverage is poor.

Staph aureus causes problems because it produces a lot of different toxins. These damage the blood cells and tissues of the udder. The sneaky thing about Staph aureus bacteria is that, as they multiply, they communicate with one another. They can wait until they reach a certain population size before they release their toxins: then the cow’s immune system is overwhelmed and she doesn’t stand as much of a chance!

If you looked at Staph aureus under the microscope, it’s classed as gram-positive bacteria: round and purple.

microscope view of gram positive and gram negative bacteria

Evil E. coli

E. coli is classed as an environmental bacteria, and is found in manure and contaminated mud and feed. Infections with environmental bacteria generally occur in the hour or two after milking when the teat canal is still closing. If cows’ udders are splashed with mud, or when the cow sits down on contaminated pasture or bedding, bacteria have the opportunity to enter the udder. E. coli is also what we call a gram-negative bacteria. Under the microscope it looks like little red rods (see picture above).

A cow’s immune system is always specifically on the alert for gram-negative bacteria. When it detects that they’re present it goes a bit nuts! It mounts a massive immune response that results in depression, recumbency, dehydration and low blood calcium (milk fever).

Do we need to know which bug is causing the problem?

The antibiotic treatment of gram-negative and gram-positive bacteria is different, and the advice about prevention of cow-associated vs environmental bacteria is also very different. As such, it’s important to know which bug is causing an issue on your farm. As we can’t tell the difference based on clinical signs, culture of milk samples is needed for diagnosis.

The Vet Group offers an in-house milk culture service and can identify the bacteria – if present – in 1 to 2 days. The photo comparison below show how we tell Staph aureus and E. coli apart.

If you have cows with toxic mastitis, talk to one of our vets about treatment. If taking a milk sample from an affected quarter prior to treatment, make sure that it’s hygienically collected (this will be difficult if the cow is down, so make it a two person job!). Place samples in the fridge before bringing into the vet clinic to prevent the growth of an contaminant bacteria.

two chromogenic agar plates showing e coli and staph growth