Staph aureus testing

Benefits of Staphylococcus aureus testing

One of the most common types of chronic mastitis is caused by the bacteria, Staphylococcus aureus (staph aureus). Often, it is subclinical, where there is neither abnormal milk nor detectable change in the udder, but somatic cell count has increased. 

Using herd test milk samples, the staph aureus test can be a convenient way of identifying whether subclinical staph aureus is a problem in a herd. It can enable more informed decisions for dry cow treatment vs culling as part of an overall mastitis management plan.

About Staphylococcus aureus

Staph aureus attacks the tissue of the udder causing production loss during infection and residual loss due to permanent udder damage.   Ongoing sub-clinical infections can result in recurrent clinical infections and the slow destruction of the udder. Infected cows may have a fluctuating cell count and intermittent shedding of bacteria. 

How Staphylococcus aureus testing works

We utilise milk samples from a routine herd test to detect whether subclinical staph aureus is a problem in a herd.

We can test a select group of animals by either:

A list selected by the vet and farmer

This will allow selection of animals based on a combination of high SCC history, clinical history, past treatments, potential new infections or any other selection criteria relevant to the herd.

OR

A list selected by LIC based on agreed SCC criteria,

The SCC threshold will be decided in consultation with the vet and farmer and a maximum number of samples for testing can be specified. A minimum number of 25 samples is required for testing.

When to test

Testing is recommended in later lactation when staph aureus is the most common mastitis causing bacteria in many herds.

Getting the results

Results will be emailed to your vet within 5-7 working days of you receiving your herd test lab strip.

LIC Validation Trials

Herd test milk samples and aseptic quarter foremilk samples were tested for S. aureus using PCR and results compared to bacteriology as the gold standard.

The sensitivity and specificity of S. aureus test was found to be 99.1% and 99% respectively for the aseptic quarter samples; however herd test milk was found to be less sensitive, with only 70% of true positive cases identified, with specificity remaining at 99%.

Limitations of the test

S. aureus is not consistently shed in the milk so at the time of the herd test it is possible that an infected cow is not shedding sufficient bacteria to allow detection. Herd test milk is a composite sample of all quarters, so the expected sensitivity will be less than individual udder quarter samples.

Book a staph aureus test

Forewarned is forearmed. Talk to your vet and get them to book a convenient staph aureus test with your next herd test, to support your culling and dry off decisions.

Email the Animal Health team or contact our Animal Health Advisors on 0800 436 362 once you have a herd testing date.