Monitoring residues of veterinary medicines in milk
When it comes to determining withdrawal periods for milk in dairy cows, we rely on a benchmark known as the Maximum Residue Limit (MRL) set by the European Commission. This standard applies across the European Union and is used by government laboratories in testing samples submitted under the national residue plan.
However, the MRLs for specific drugs may not align with the test standards used by creameries to test milk for inhibitory substances, including antibiotics. This means that dairy farmers supplying milk to creameries might need to take additional precautions to meet the creamery milk quality requirements.
Residue testing in Ireland
In Ireland, residue testing of milk, honey, eggs and meat is carried out in line with the national residue plan, regulated by the Department of Agriculture, Food and the Marine in collaboration with the Food Safety Authority. The benchmark for testing is the Maximum Residue Limit (MRL), which is established for each drug or drug class used in a veterinary medicine.
These limits developed by the European Medicines Agency (EMA) following a rigorous scientific review of the drug’s toxicology, as well as its absorption, distribution, metabolism and elimination in treated animals.
Internationally, the same approach is followed by the world body, Codex Alimentarius, in establishing MRLs. The MRLs set are taken into consideration when establishing MRLs for the European Union. Once adopted by the EU, these MRLs become legally binding limits that protect public health. These limits are updated periodically and published by the EU Commission Further information is available here. Only when an MRL has been established can the HPRA authorise veterinary medicines containing the substances concerned, on foot of an application from an animal health company.
Setting withdrawal periods
The HPRA uses the EU’s MRL to determine withdrawal periods for veterinary medicines. Companies seeking marketing authorisation for veterinary medicines intended for use in food-producing species must conduct residue studies on treated animals under specified dosage conditions.
The HPRA evaluates the data from these studies against the applicable MRLs, using the approach specified by the EMA. From this we establish a withdrawal period for each medicine on the basis of how long it takes for residues to fall below these values.
It is important to recognise that the standards those used by Irish creameries and milk processors are not necessarily the same as the MRLs in question. These tests might be highly sensitive to some drugs such as penicillins and cephalosporins, while being less sensitive to others. This could lead to milk failing routine screening even when the farmer has followed the recommended withdrawal period.
Creameries and milk processors set out their requirements for milk quality in their contracts with farmers who supply them with milk. These standards generally include specifications for the composition of the milk itself such as percent protein and fat, as well as other parameters such as somatic cell counts and residue specifications such as all milk must pass the creamery’s own test. The HPRA is not involved in this commercial area.
It is important to note that withdrawal periods on medicines authorised by the HPRA:
- Are invalid if a lower residue limit is applied for testing milk.
- Are invalid if the veterinary drug is used at a higher dosage than that specified.
- Are subject to revision (infrequently), based on new residue studies being conducted or updates to the EU MRL value.
- Might not be sufficiently long when different veterinary medicines are used concomitantly or within a short period of time to treat the same animal.
Actions for farmers and veterinarians
To address these changes, we recommend the following precautionary measures to farmers and their health-care professions involved in supplying milk to creameries:
- Farmers should remain vigilant about the use of veterinary medicines, especially antibiotics, to avoid unwanted residues.
- Follow the directions of use stated on the package leaflet unless directed otherwise by your veterinary practitioner. However, note that the prescribed withdrawal periods may not align with more stringent tests used by milk processors.
- Creameries with different residue standards should clearly communicate these standards to farmers and their veterinary practitioners.
- Consider increasing the stated withdrawal period where the creamery’s standard is more sensitive than the MRL.
- If a residue violation occurs despite having used the medicine as recommended, users of veterinary medicines should consult their veterinary practitioner, who should report the issue either to the company concerned or to the HPRA. We will treat the matter as a suspected adverse event and follow up accordingly.