Yesterday, I explained why and how we use antibiotics to treat a cow who falls ill in the herd, together with what we do to make sure no antibiotics get in the milk that leaves the farm.

In this post, Fonterra’s quality manager for milk supply, Sarah Carter, answered a few questions about how the milk is screened for antibiotics by the milk factory.

MMM: Why is it important to keep antibiotics out of milk?
SC: Customers, consumers and markets have very clear requirements that dairy products are to be free of antibiotic residues. The two main reasons for this are: the risk of causing allergic reactions in humans (e.g. from penicillin), and the concern about a build-up of antibiotic resistance as a result of consumption of dairy products containing low levels of antibiotics.

MMM: What does the law say about antibiotics in milk?
SC: In Australia, the Australian Pesticides & Veterinary Medicines Authority (APVMA) assesses agricultural and veterinary chemicals, such as cattle antibiotics, as being suitable and safe for use. They set Maximum Residue Limits (MRLs) after undertaking a thorough evaluation, including a dietary exposure assessment. These MRLs apply to domestically-produced foods, and are set well below the level at which any residues would be harmful to human health. The MRLs are set at levels which are not likely to be exceeded if the approved label instructions on the antibiotic product are correctly followed.

MMM: How and when is the milk tested?
SC: Most, if not all, dairy companies test tankers of milk for antibiotics prior to unloading at the factory, to avoid any contaminated milk entering the supply chain.

A number of dairy companies will also have the individual farm milk samples randomly tested during each month to further discourage farmers from taking a risk and allowing a vat-load of milk to be collected where perhaps a treated cow had been accidentally milked.

At Fonterra, we have both these measures in places – we are very clear that to maintain and build the market relevance of our dairy products, dilution with milk from other farms in the tanker is not the solution.

MMM: How sensitive are the tests?
SC: There is quite a wide range of tests available to detect antibiotics in milk, and the detection limits for antibiotics vary between tests. All dairy companies have their antibiotic testing procedures audited by the relevant state dairy regulatory authority (such as Dairy Food Safety Victoria) to ensure that their chosen test method is suitable for purpose and based on a risk assessment.

Different test methods will have different sensitivities to the various active ingredients found in commonly-used antibiotics – there is a technical information note available on the DFSV website which lists the common tests and their detection limits.

MMM: What happens if antibiotic residues are detected?
SC: If antibiotics are detected at the tanker level (prior to unloading into the factory), the entire tanker load is rejected and the milk disposed of (e.g. via the factory environmental management system).

Traceback testing is undertaken on all farms on that tanker load, to identify the source of the issue. We then undertake an on-farm investigation to get to the root cause of the problem and put measures in place to ensure it doesn’t happen again. All antibiotic-positive tankers must be reported to the state dairy regulatory authority, and followed up with a report stating the findings of the on-farm investigation.

If antibiotics are detected on a random farm sample test, we again undertake the on-farm investigation to help the farmer identify what went wrong. We also undertake a trace-forward to check for any impacts to products manufactured from this milk.

Farmers receive a penalty for supplying antibiotic-contaminated milk, and this penalty increases significantly if it happens again – fortunately, repeat offenders are incredibly rare, which demonstrates that the investigation and corrective action process achieves what it’s meant to.

At Fonterra we also encourage our farmers to get in touch with our SupportCrew milk quality specialists, who can assist farmers with advice and support to minimise the risk of mastitis in the first place.

Thanks Sarah!