Investigation of the persistence of triclabendazole residues in bovine milk following lactating-cow and dry-cow treatments

Abstract

Triclabendazole is a flukicide used in the treatment of liver fluke in cattle. However, its use in the treatment of liver fluke is prohibited in dairy cows. In this work, two independent studies were designed to investigate the persistence of triclabendazole residues in milk following the administration of 10% Fasinex® as dry-cow and lactating-cow treatments. In the dry-cow study, 36 in-calf dairy cows were treated with a commercial product, 10% Fasinex^®, at drying-off and three triclabendazole residues (triclabendazole, triclabendazole sulphoxide and triclabendazole sulphone) were monitored in the milk following calving, approximately 60 days post-treatment. No residues were measurable in the milk of the 36 cows tested – the LOQ of the method was 1.00 µg kg⁻¹. In the lactating-cow study, the persistence of four triclabendazole residues was investigated in the milk of six dairy cows. The highest levels of triclabendazole, triclabendazole sulphoxide, triclabendazole sulphone and keto-triclabendazole residues measured in individual milk samples were 244, 525, 1710 and 16 μg kg⁻¹, respectively. Residues of triclabendazole, triclabendazole sulphoxide, triclabendazole sulphone and keto-triclabendazole were detectable in milk for up to 5.5, 15.5, 20 and 5 days post-treatment, respectively. Triclabendazole sulphone was found to be the most important residue, accounting for >87% of marker residues at ≥3.5 days following drug administration. These results indicate that following treatment at drying-off, triclabendazole residues in milk post-calving are well below the current MRL. Therefore, triclabendazole is a suitable flukicide for use during the dry period.

Keywords:

• triclabendazole
• bovine milk
• residues
• anthelmintic
• flukicides
• UHPLC-MS/MS

Acknowledgements

This work was co-funded by the Dairy Levy Research, The Irish Department of Agriculture, Fisheries and Food under the Food Institutional Research Measure as part of the National Development Plan (Projects 06RDTMFRC434) and by EU Sixth Framework programme on Food Quality and Safety, ProSafeBeef project FOOD-CT-2006-36241. The authors acknowledge Teagasc staff at Ashtown, in particular Martin McCormack, and the farm staff at Moorepark and Ballydague, in particular Noel Byrne, Billy Curtin and John Paul Murphy, for their valuable assistance. Clare Power was in receipt of a Teagasc Walsh Fellowship.