From the ingredients on the bag: Wheat middlings, corn distillers dried grains with solubles, corn, soybean meal, L-Lysine, DL-Methionine, calcium carbonate, Sodium Bentonite, salt, ferrous carbonate, ferrous sulfate, copper sulfate, Manganous oxide, manganese sulfate, zinc oxide, zinc sulfate, Cobalt Carbonate, calcium iodate, sodium selenite, vitamin a supplement, vitamin d3 supplement, vitamin e supplement, menadione dimethylpyrimidinol bisulfite, thiamine mononitrate, riboflavin supplement, niacin supplement, choline chloride, calcium pantothenate, pyridoxine hydrochloride, folic acid, biotin, vitamin b12 supplement, propionic acid (a preservative).
2nd and 3rd ingredients, so I'd say a high percentage of the product is comprised of corn.