Well the list of ingredients ....
Timothy Grass Meal, Soybean Hulls, Soybean Meal, Wheat Germ, Xanthan Gum, Calcium Chloride, Cane Molasses, Salt, Potassium Chloride, Hydrated Sodium Chloride, L-Ascorbyl-2-Polyphosphate, Soybean Oil, Papaya, Pineapple, Natural Flavor, Oat Groats, Wheat Middlings, Yeast Culture (dehydrated), Limestone, Vitamin E Supplement, Choline Chloride, Zinc Proteinate, Zinc Sulfate, Ferrous Sulfate, Niacin, Copper Sulfate, Selenium Yeast, Vitamin A Supplement, Folic Acid, d-Calcium Pantothenate, Copper Proteinate, Riboflavin Supplement, Manganese Proteinate, Biotin, Manganous Oxide, Thiamine Mononitrate, Magnesium Sulfate, Vitamin B12 Supplement, Sodium Selenite, Pyridoxine Hydrochloride, Cobalt Carbonate, Vitamin D3 Supplement, Calcium Iodate, Ethylenediamine Dihydriodide, Bacillus coagulans, Enterococcus faecium, Lactobacillus acidophilus, Lactobacillus plantarium, Lactobacillus bulgaricus.
..... the main ingredient is hay, as you say. Then there's the rest which I guess you could be allergic to?