20 parts per billion isn't "consuming" aflatoxin-laden feed - it's eating regular feed with trace contamination. That there are guidelines for achieving this "safe" dilution makes you wonder why the effort is being spent there instead of using the grain for other purposes. Also worth reminding that these measurements are taken via random sampling - as per my cyanide example.

Dont intentionally feed aflatoxins to dairy animals! (or any animals, really...)