Corn is corn. Your birds are going to find a LOT worse if they free range. Aflatoxins are in a pink mold that naturally occures on ALL corn. It is more prevaliant in cool moist falls and if you look at the kernals, it will be pink. Most often is on the tip or butt of the ear but is can be all over.
I taught highscool Ag and FFA for many years. I would not hesitate to use it unless it LOOKS spoiled. Even then chickens naturally will scratch in cow manure to get undigested kernals of grains.