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Antihelmintic Residues In Milk

12 April 2011

Michelle Whelan won the RDS gold medal for best presentation and the IFSTI president’s medal for best food science and technology presentation at the annual Teagasc Walsh Fellowships seminar in the RDS for her presentation on ‘Determination of anthelmintic residues in milk using UPLC-MS/MS with rapid polarity switching’. Here she explains the significance of the research to the Irish dairy industry.

Anthelmintic drugs are widely used to control roundworm, tapeworm, liver-fluke and stomach-fluke infections in food-producing animals. However, only a limited number of drugs are licensed for use in lactating animals and have a maximum residue limit (MRL) listed under European Council Regulation 470/2009/EC. There is concern that the limited number of licensed products, and the development of drug resistance, could increase the potential for off-label applications in animals. A number of these substances have undesirable toxic effects at high doses in laboratory animals, but levels detected in food are generally well below toxicity thresholds. However, integrated parasite control programmes are an important part of modern agriculture and are necessary to maintain animal health and production yields.

A new rapid analytical method was developed to test for 38 anthelmintic drug residues in milk in a 13-minute run. It is the only test method available for the simultaneous detection of both worm and fluke products. The benefit of this new extraction method is that it is very quick, with few steps, and allows 36 samples to be tested daily. This new method is also extremely sensitive and can detect residues to trace levels. In addition, the amount of solvent used is greatly reduced and very little waste is generated due to the quick extraction and rapid analytical method.

The method, developed at Teagasc Food Research Centre, Ashtown, was transferred to the National Reference Laboratory (NRL) for anthelmintic drugs in late 2008 and was accredited by the Irish National Accreditation Board (INAB) to ISO 17025. It has been applied to milk samples collected as part of official food inspection.

This resulted in the detection of low levels of flukicide residues in milk, which led to several veterinary products being restricted in dairy animals by regulatory agencies (Irish Medicines Board [IMB]). In subsequent research, the method was used to investigate the persistence of flukicides in the milk of dairy cows treated during lactation with the following drugs: nitroxynil, oxyclozanide, clorsulon and triclabendazole.

These studies generated new knowledge, which can be used by risk assessors, decision makers and animal health companies to set suitable withdrawal times for veterinary medicines to ensure the safety of milk. The results from this research on the persistence of drugs in dairy animals can also support the development of new veterinary medicinal products for the treatment of infections in dairy cows. This will lead to improved labels on veterinary medicines, which inform farmers to adopt best practice.

This new sensitive test method used to monitor the purity of milk has improved the safety of Irish milk, and supports the export of Irish produce. This research will underpin the green image of Irish dairy products to ensure consumer confidence and safeguard international investment in the sector.

One of the major outcomes of this work was the setting of provisional MRLs by the European Medicines Agency (EMA) for triclabendazole and closantel in milk following requests by the IMB under Article 9 of EC regulation 470/2009/EC. This is the first time a government agency has proactively sought for an MRL to be established. This is one of the most important developments from this work.

April 2011

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