Two experiments were made. In experiment 1, dairy cows in early lactation (2 to 4 weeks) and dairy cows in late lactation (34 to 36 weeks) were given aflatoxin B1 (AFB1) at a level of 34 to 39 mug/day by feeding them contaminated compound food. The aflatoxin M1-content (AFM1) of raw milk was determined four times during the experimental period of 14 days. The milk yield was measured daily. The carry-over rate of aflatoxin was proportionately 0.062 and 0.018 for cows in early and late lactation respectively. This difference was not only due to milk production level but possibly also associated to AFB1 liver metabolism. In experiment 2, eight high (40 kg milk per day) and eight low (16 kg milk per day) milk yielding cows, carry-over of AFB1 from compound food into AFM1 in milk was measured at different levels of AFB1 intake ranging from 7 to 57 mug/day. Independent of AFB1-intake, high-producing dairy cows had a higher carry-over rate than low producing animals (proportionately 0.038 v. 0-025). Carry-over of AFB1 to AFM1 was linearly correlated with milk yield. Variations in the level of AFM1 in milk of individual cows were not due to variations in milk yield. The relationship between AFB1 intake per day and AFM1-content in milk per kg could be described by the formula: AFM1 (ng/kg milk) = 1.19 AFB1 intake (mug per cow per day) + 1.9. This means that in order to produce milk with less than 0.05 mug AFM1 per kg milk the average daily individual intake in a herd should be limited to 40 mug AFB1 per day. As dairy cows in their early to mid lactation period consume large quantities of compound food, a maximum level of AFB1 in dairy foods has to be set at an acceptable daily intake (ADI) value to guarantee that AFM1 levels in milk do not exceed tolerable levels.
