Detection of antibiotics in sheep milk by receptor-binding assays

Receptor-binding assays to detect antibiotics in sheep milk were evaluated. Specificity of the Betastar Combo, SNAP and TwinsensorBT tests was optimal using inhibitor-free bulk sheep milk (99–100%), and no differences between the visual or instrumental classification were found. For individual sheep milk free of antibiotics, specificity was elevated by the Betastar Combo and SNAP tests. However, lower specificity was obtained by the TwinsensorBT test, especially in the last weeks of the lactation period. Regarding cross-reactions, interferences related to drugs other than β-lactams and tetracyclines were not detected. Furthermore, the use of azidiol, as a preservative of milk, had no effect on the test. In all cases, the detection capability was able to detect most β-lactams and tetracyclines at or below maximum residues limits. The receptor-binding tests evaluated showed a very good performance in the detection of antibiotics in sheep milk, thus being suitable for milk quality control programmes.