Usefulness of the analytical control of aflatoxins in feedstuffs for dairy cows for the prevention of aflatoxin M1 in milk

Aflatoxin M₁ (AFM₁) is a hydroxylated metabolite of aflatoxin B₁ (AFB₁) and can be excreted in milk of cows after consuming aflatoxin (AF)-contaminated feed. The aim of this research was to assess the levels of total AFs in samples of feedingstuff for dairy cows (n = 193) and the levels of AFM₁ in raw bulk tank milk samples (n = 375), in order to estimate the ratio of "AFB₁ feed input" versus "AFM₁ milk output" in four specific regions of Spain. Moreover, the correlation between the raw materials used as ingredients of the total mixed ration (TMR) and the presence of AFs was studied. About one-third (34.7%) of the feed samples were positive for total AFs in a range of 0.05-6.45 μg/kg, and 12.4% were positive for AFB₁. AFM₁ was detected in 18.9% of bulk milk samples, with concentrations ranging from 0.009 to 1.36 μg/kg. While none of the feed samples exceeded the European Union (EU) maximum content for AFB₁ in feedingstuff for dairy animals of 5 μg/kg, three bulk milk samples exceeded the EU maximum level for AFM₁ in milk of 50 ng/kg. The transfer ratio AFB₁/AFM₁, which was derived from AFB₁ levels in feed, AFM₁ levels in bulk tank milk, feed intake, and milk yield data, was 0.6-6%, which corresponded well with the range of published carry-over data for aflatoxins. Statistical analyses showed that the main sources of AFB₁ in TMR were maize silage, bagasse, soya bean husk, maize, alfalfa hay, cotton seed and compound feed, thus special attention should be paid in controlling these raw materials when used in TMR preparation. Although the analysis of AFs in feed did not correlate with the presence of AFM₁ in milk, monitoring feedstuffs is a useful tool in order to try and minimise AF-contamination of milk.