The Carry-Over of Aflatoxins in Dairy Feed to Milk of Modern Holstein Dairy Cow

Aflatoxins are hepatotoxic and carcinogenic secondary metabolic products from the fungal species Aspergillus flavus and Aspergillus parasiticus. Aflatoxin M1 (AFM1) is the major metabolite of Aflatoxin B1 (AFB1) present in mammalian milk. The US Food and Drug Administration (FDA) dictates a maximum allowable concentration of 20 microg/kg total aflatoxin in food and feed intended for dairy consumption, and 0.5 microg/kg AFM1 in milk and milk products. The European Commission dictates a maximum allowable concentration of 4 microg/kg total aflatoxin and 0.05 microg/kg AFM1 respectively. The carry-over of AFB1 (the amount of AFB1 in the feed that is excreted as AFM1 in the milk) is a major factor used to create regulations for acceptable AFB1 concentrations in dairy cattle feed. It has been observed that higher producing dairy cows (30-40 kilograms of milk per day) have a higher carry-over rate, but current regulations use older studies using low-producing dairy cows (10-20 kilograms of milk per day) as a reference for risk. The objective of this project was to measure the carry-over rate of AFB1 from feed to AFM1 in the milk of modern, high-producing US Holsteins milked three times a day to provide a more relevant assessment for current regulations. Corn naturally infected with aflatoxin-producing fungi was used to imitate a real-world contamination scenario, an approach applied in only one previous study (Frobish et al., 1986). Three replications of a feeding trial to test carry-over in high-producing dairy cows were completed; each using 12 high-producing dairy cows in early- to mid-lactation, fed naturally contaminated corn meal top-dressed on their daily total mixed ration. Cows in each replication were assigned to: control (0 microg/kg), low (10 microg/kg), or high (20 microg/kg) AFM1 groups. Feed and milk samples were taken for seven (replicates 1 and 2) or two (replicate 3) days and analyzed with a VICAM fluorometer. Using linear regression, the direct carry-over rate was 6.5%, much higher than the 1 to 2% estimated by previous researchers using low-producing dairy cows. These findings suggest that the US regulatory limit of 20 microg/kg of total aflatoxin in the feed is not a guarantee of protection against violating the regulatory limit of 0.5 microg/kg of AFM1 in milk of high-producing dairy cows.