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.