Aflatoxin M1 (AFM1) is a hydroxylated metabolite of aflatoxin B1 (AFB1) that can be excreted in milk of cows after consuming contaminated feed. The aim of this study consisted of a field monitoring to assess the contamination levels of AFB1 in 60 feed samples from two feeding systems for high-yielding dairy cows and of AFM1 in the corresponding raw milk samples. The aflatoxins were analyzed by in-house validated methods based on high-performance liquid chromatography (HPLC) with fluorescence

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... ection. AFB1 was detected in 55% of feed samples (mean 0.61 μg/kg, with 2 samples exceeding the European Union (EU) maximum level set at 5 μg/kg), with greater incidence and concentration in compound feed than in unifeed rations (p < 0.05). AFM1 was detected in 38.3% milk samples (mean 12.6 ng/kg, with 5 samples exceeding the EU maximum level set at 50 ng/kg), with a higher occurrence in milk of cows fed compound feed, as well as in spring milk compared to that produced in winter. The overall transfer ratio of aflatoxins from feed to milk was 3.22%, being higher in cows fed with compound feed and in spring milkings. In a selection of positive matched samples (n = 22), the ratio AFM1/AFB1 exceeded the European Food Safety Authority (EFSA) estimated 6% threshold for high-yielding dairy cows.