Aflatoxin is primarily a problem in corn. Corn is a large grain that more easily stress cracks. The fungus (a flavus) causes aflatoxin which enters via stress cracks, etc.. Human consumption is limited to 20 parts per billion. Dairy cattle consumption can produce aflatoxin in the milk. Milk producers had/have a limit of one half of one part per billion. Some animals have higher levels of approved consumption.
The company I worked for for 45 years tested lots of corn for aflatoxin and fumonisin (another mycotoxin). For many years now, some companies have produced crop treatments to reduce