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.

Investigation of the Persistence of Closantel Residues in Bovine Milk Following Lactating-Cow and Dry-Cow Treatments and Its Migration into Dairy Products

“…However with skim milk powder, manufactured from skim milk, the triclabendazole residues concentrated in the powder, despite the relatively low levels of residue detected in the starting skim milk. 22 Similar results were found with rafoxanide regarding residues migrating in cream, butter, and cheese as well as skim milk powder, despite the relatively low residue levels in the starting skim milk. 29 For both triclabendazole and rafoxanide, there were no significant differences in residue levels between products manufactured from pasteurized and unpasteurized milk, nor were there any significant differences in residues in butter and cheese stored at −20°C for up to 1 year.…”

Investigation of the migration of triclabendazole residues to milk products manufactured from bovine milk, and stability therein, following lactating cow treatment

“…The following analytical method performance parameters were investigated: within-laboratory reproducibility, within-laboratory repeatability, specificity, linearity, and accuracy. The validation of the method for the determination of TCB residues in milk has been described elsewhere (Power et al, 2013).…”

“…Sample analysis was carried out using the UHPLC-MS/MS system described elsewhere (Power et al, 2013). In brief, separations were performed using a Waters (Milford, MA) Acquity UPLC system comprising a stainless steel HSS T3 analytical column (100 mm × 2.1 mm, particle size 1.8 μm) equipped with an in-line filter unit containing a 0.2-μm stainless steel replacement filter maintained at a temperature of 60°C, and the pump was operated at a flow rate of 0.6 mL/min.…”

“…Purified extracts were analyzed for TCB, TCB-SO, TCB-SO 2 , and keto-TCB residues. Analytes were detected using a Quattro Premier XE triple quadrupole mass spectrometer (Waters, Milford, MA), equipped with an electrospray ionization source operating in positive mode; MS conditions are outlined by Power et al (2013).…”

“…Keto-TCB constituted 61 to 82% (1,282 or 1,724 μg/kg) of the total radioactive residues. More recently, Power et al (2013) showed that the mean concentration of summed TCB residues expressed as keto-TCB was 1,703 μg/kg on d 2. This suggests that TCB, TCB-SO, TCB-SO 2 , and keto-TCB are the major metabolites that occur in milk.…”