Check the "ingredients" list. You'll most likely find "corn" or "soy" or a "gluten meal" listed within the top 3 or 4 ingredients. These vegetable ingredients contain protein... but it cannot be digested by ferrets. Ferrets are obligate carnivores. Their digestive tract is not designed to extract nutrition from vegetable sources. So that 40% protein is only (maybe at most) 30% animal protein that is nutritional for ferrets. Since the extra vegetable protein cannot be digested, it passes through as poop without placing an extra burden on kidneys. (I'm not a nutritionist, so this is a fairly broad explantion!) http://www.totallyferret.com/nutrition.html is a very informative article on ferret nutritional needs. Even though it's written by Tom Willard who (understandably) pushes his brand of food, the fact remains that he IS the ONLY one who has done any REAL and documented research on ferret nutritional needs. Debi Christy Ferrets First Foster Home Practical & easy training, care, & maintenance articles available at http://www.geocities.com/ferretsfirst/ [Posted in FML issue 3668]