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Avoiding Residues in Milk

One form of contamination could be from residues of medicines that are used to treat animals. When veterinary medicinal products (VMPS) are licenced, they undergo strict testing. Part of which is to set the Maximum Residue Levels (MRL). This is the level of drug that is allowed to be in the product but, is still safe for the consumer. This is then worked back to give the withdrawal time for the medicine, during which time the product needs to be discarded as unfit for human consumption. Indeed, it is a criminal offence to place this product into the food chain.

Why are MRLs important?

As well as having this legal obligation, traces of drug residues above the MRL could cause consumers with hypersensitivity or allergies to certain drugs to have a reaction and become ill. Yoghurt and cheese production could also be effected if the residue levels in the milk are too high. The bacteria necessary for the culture could be inhibited and not able to develop. Of course, there is a wider representation risk to the industry in that milk is seen as one of the most wholesome, pure nutrients and, it is important that its integrity is protected.

Record keeping is key

When administering medicines we all know the importance of record keeping. It is a legal requirement and can be handwritten in a booklet or input in to the farm management software. The information required includes the ear tag number/management or freeze brand of the animal, the medicine used (name, batch number, expiry date), route and volume administered along with the calculated withdrawal time before milk/meat can re-enter the food chain. This is always the first reference point.

Not so simple

However, life is never as simple as keeping rigidly to the instructions provided on the label or the packaging or label. The protocols for treating a particular condition may be set out differently by your vet in your herd health plan and it may be routine to use products outside the data sheet recommendation, so called ‘off label’ use. This could be as shown below:

  • Extended treatments (4 days intramammary tubes instead of 3).
  • In combination with another systemic treatment such as antibiotic injection or NSAID (which is not specifically licenced as a combination therapy)
  • Different route of administration

All these indications should only be authorised by your vet and the withdrawal time would alter to the industry standard of species withdrawal time. In this instance, the default would be 7 day’s milk and 28 day’s meat withdrawal. It is good practice to subject the milk to a cow-side inhibitory substance test, such as Delvo SP, to be absolutely sure before the milk goes back in the tank. As always, your vet will be able to advise on any deviation that needs to be applied to the stated withdrawal time of medicines used.

Main sources of contamination

It comes as no surprise that the main sources of bulk tank contamination with residues and ultimately, failure, is intramammary preparations, in both Dry Cow and Lactating Cow form.

It’s worth noting that it takes just 1g of Penicillin to put 250,000 litres of milk over and above the legal limit for residues. In context, some of the lactating tubes contain 60% of this weight of product and dry cow tubes a similar amount but, in a longer releasing formulation. Injectable Antibiotics are another source of contamination. Other risks are posed by teat disinfectants and creams, together with intra-uterine pessaries and ‘wash out’ solutions.

We know which animals have been treated and what products we have used so it ‘should be’ simple to isolate these from the supply chain. Should be is the operative phrase here, and human error is the main cause of residues entering the bulk tank, as can be seen below.

  • Poor communication between staff
  • Poor treatment records
  • Poor identification of treated cows
  • Accidental milking of recently dried off or cows under treatment
  • Accidental transfer of contaminated milk
  • Inadequate cleansing and disinfection of equipment used to milk treated animals/plant contamination.
  • Failure to observe the correct withhold time
  • Only withholding milk from quarter under treatment
  • Milking of recently purchased cows with unknown history/or not tested prior to introduction to the milking herd
  • Lack of clear information on withhold times and incorrect application of withhold periods following off label use.
  • Prolonged excretion of antibiotics.
  • Deliberate contamination

Control points

The list is not exhaustive but, by looking at each control point, it should be straightforward to produce a risk analysis and a set of pitfalls to avoid. At the very least, it should minimise the risk.

  1. Poor Communication. This is linked to identification. After treating an animal, details should be entered into the treatment records in the medicines book. This should be closely followed by inputting the information onto a visible board for all to see at the level of the parlour. (Remember that if you have workers who do not have English as their first language they need to be made aware as well). A useful resource, Best Practice to Prevent Medicine Residues in Milk, is available from AHDB Dairy website in 5 languages.
  2. Identification. This needs to be applied at the time of treatment and should be doubled up in case the first method fails. Tail tape (again double) together with spray marking the udder and hocks of the cow should be employed. Some of the pharmaceutical companies supply Velcro ankle straps that can also be used. Cows, following drying off, should be removed from the herd and placed in their own group.
  3. Isolate cows receiving treatment. Ideally, any cows receiving treatment should be milked last, once the main herd has been milked. However, this is rarely practical. It is important to have a dedicated and fully isolated system, via a dump bucket, to milk these cows. Full cleansing with disinfectant and hot water should be undertaken of any pipes, clusters and claw pieces if the unit is then to be returned to the normal milking routine. If you don’t have a dedicated dump bucket, take extreme caution to ensure the contaminated milk is not released into the system and, once again, thorough cleaning following use should be undertaken.
  4. Care should be taken with cows that may calve down before their expected due date with cross reference made to the date of withdrawal following infusion. Remember that, even if the animal has had the requisite withdrawal, the milk should not be consigned for 4 days post calving (milk hygiene regs).
  5. If in doubt, test using Delvo SP

The ultimate responsibility to consign product that is fit for purpose, rests with the Food Business Operator (FBO). In this case the farmer. On farm testing using tests such as Delvo SP offers a rapid solution to checking milk is fit to be consigned and provides assurance that milk is free from a broad spectrum of residues. More advanced testing, using InfiniPlex in a laboratory setting, allows for detection of a range of 91 individual antibiotic residues, as well as those of anti-inflammatory anthelmintic and other compounds. It is highly sensitive but, allows further investigation in circumstances where there is a residue failure.

If you do suffer a bulk tank failure then this type of test will be used to try and identify the product that is likely to have caused the failure. You and your vet will work through a questionnaire, such as the BCVA Bulk Tank Failure Protocol. The Delvo SP test, in this instance, would give you a failure, whereas InfiniPlex may identify failure to B lactams, neomycin, novobiocin and methyl prednisolone, a unique combination of medicinal products only available in one specific lactating cow tube.

Ultimately, we should all take our responsibilities seriously to ensure that residues do not enter the food chain, and when you pour your cold fresh milk on your morning cereal it is just that.

Further training can be gained by accessing MilkSure and completion of a validated Red Tractor approved Medicines Training course. Give us a call if you would like further details or to discuss any issues you may have.

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Avoiding Residues in Milk
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Forth Valley Veterinary Practice Stirling

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