Re-evaluation of aflatoxin M1 transfer into milk of high-yielding cows considering ration composition

Abstract

Aflatoxin M1 (AFM1) is a metabolite of aflatoxin B1 (AFB1) and can be detected in milk when AFB1- contaminated feed is used. The European Commission (EC) has set maximum levels for AFM1 at 0.050 µg/kg in milk and 0.025 µg/kg in infant formula and follow-on milk. Moreover, a maximum residue limit of 5 μg/kg AFB1 in compound feed for dairy cattle has been established in the European Union, assuming transfer rates into milk of 2–3%. However, it has been published that transfer rates of approx. 6% may occur for high yielding cows (> 30 kg milk/day). A higher proportion of concentrates in the ration may ultimately result in a lower rumen pH or a shift in the rumen microbiome, thereby leading to changes in the rate of AFB1 absorption. Therefore, re-evaluation of the AFM1 transfer rate is of major importance to determine the acceptable AFB1 intake levels from feed. The present study analysed the influence of feed composition on the transfer rate of AFB1 to AFM1 into milk. Cows were fed a daily low (7.5 kg) or high (12.5 kg) concentrate ration, and AFB1 (50 µg/day) was administered orally once daily for 10 days. AFM1 transfer rates ranged from 1.28 to 3.89%, but were not significantly influenced by the ration. Moreover, the addition of the aflatoxin binder Admonil between days 8 and 10 led to a strong reduction in AFM1 concentrations in the milk of both groups. Based on the confirmed mean transmission rates of 2.3–2.5%, it can be concluded that the maximum limits for AFM1 in milk (0.050 µg AFM1/kg) according to Regulation (EC) 165/2010 will not be exceeded unless AFB1 is introduced in feed in addition to the regulated concentrates.