Since aflatoxins have been shown to be carcinogenic in laboratory test animals FDA set action levels at 20 ppb for foods such as corn fed to dairy cows because of the risk of aflatoxin getting into milk. The action level for aflatoxin in milk is set at 0.5ppb. Livestock producers buying this year's corn will want to check for the presence of aflatoxin before feeding to cattle, especially lactating dairy cows.
Several methods exist for checking for the presence of aflatoxin.
Screening with a black light. A sample of corn is cracked and placed under the black light. A by-product of aspergillus flavus, kojic acid is produced. Under UV light the kojic acid gives off a yellowish-green florescence. This screening suggests indirectly that aflatoxin is present.