You can sift through the whole new bag of feed but that's labor intensive. When you feed just casually look at the feed, if you see anything that looks like this then I would suspect the feed would be contaminated.
Sometimes the fungus won't attack the whole grain, it usually only attacks the germ or the inner most part of the grain, so only a 1/4 to 1/3 of the grain will appear darkened.
Sometimes the fungus won't attack the whole grain, it usually only attacks the germ or the inner most part of the grain, so only a 1/4 to 1/3 of the grain will appear darkened.