Transfer of the coccidiostats monensin and lasalocid from feed at cross-contamination levels to whole egg, egg white and egg yolk

Recent legislation has addressed the unavoidable carry-over of coccidiostats and histomonostats in feed, which may lead to the presence of residues of these compounds in eggs. In this study, laying hens received cross-contaminated feed at a ratio of 2.5%, 5% and 10% of the therapeutic dose of monensin and lasalocid for broilers. The eggs were collected during the treatment and depletion period and were analysed using liquid chromatography-tandem mass spectrometry. The different egg matrices were separated and analysed during the plateau phase. High lasalocid concentrations, which exceeded the maximum residue level, and low monensin concentrations were found in whole egg. Plateau levels were reached at days 7-9 for lasalocid and at days 3-5 for monensin. For lasalocid, the highest concentrations were measured in egg yolk; residue concentrations in egg white were very low.