Aflatoxin conversion by dairy cattle consuming naturally-contaminated whole cottonseed

Whole cottonseed determined to have aflatoxin B1 (AFB1) levels of 5, 31, 104, 280, and 560 μg/kg was fed as 15% of the total dairy ration to a commercial herd of 90 grade Holstein dairy cattle for 70 d. Milk from the bulk tank was sampled either daily or after each milking and analyzed for aflatoxin M1 (AFM1). The ratio for AFB1 in the dairy ration to AFM1 in the milk averaged 75 to 1 under conditions and at levels tested with no consistent relation to the level of AFB1 in the feed. Approximately 1.6% conversion occurred during the steady state of consumption and secretion. The federal action level of 0.5 μg AFM1/L of milk would be produced by cows consuming a ration containing 15% whole cottonseed contaminated with approximately 250 μg AFB1/kg.