Aflatoxin Residues in Milk of Dairy Cows after Ingestion of Naturally Contaminated Grain

Thirty-two lactating Holstein cows, blocked according to level of milk production, were fed cottonseed meal contaminated with aflatoxin B₁, (AFB₁) (0, 94, 241 and 500 μg/kg) as 20% of their ration (equivalent to 0, 20, 48 and 104 μg/kg in complete feed). Within 12 h, aflatoxin M₁ (AFM₁) appeared in the milk of all cows receiving contaminated feed. The mean AFM₁ concentrations in the milk approached steady-state conditions (0.35, 0.63 and 1.61 μg/L for treatments of 20, 48 and 104 μg AFB₁/kg, respectively) at 24 h and returned to the Food and Drug Administration action level of 0.5 μg/L or lower within 24 h after removal of the contaminated feed. The ratio of AFB₁ in the feed to AFM₁ in the milk averaged 66:1. The mean percent of daily AFB₁ intake that was transferred to AFM₁ was 1.74. This value was unaffected by the concentration of AFB₁ in the feed (1.89, 1.55 and 1.81% transferred for treatments of 20, 48 and 104 μg AFB₁/kg, respectively). Although increased milk production had no effect on the concentration of AFM₁ in the milk, it had a positive effect (P ≤ 0.01) on the percent of AFB₁ intake transferred to AFM₁ (2.14 vs 1.35%). In a second trial, 16 additional cows were fed either naturally contaminated cottonseed meal or corn (44 and 49 μg/kg, respectively, on a complete feed basis). The percent of AFB₁ intake secreted as AFM₁ was affected (P ≤ 0.02) by the source of contamination (1.73 vs. 1.32% for the cottonseed meal and corn treatments, respectively). The AFM₁ concentrations in the milk were not significantly different (P>0.05).