Ideally then, the protein source should be the first listed ingredient in a bag of dry cat food in a "maintenance" diet, followed by secondary protein sources, if included, then whatever carbohydrate fillers are included, oils or fat, other ingredients, such as fruits and vegetables, a form of preservative, and added vitamins and minerals, including taurine.
I've chosen three foods to compare. The first (featured here) is a popular 'premium' supermarket brand of cat food. You don't need to know the brand name, because after you learn these definitions, and learn to read the rest of the label, you will be well-equipped to make educated food choices for your cat.
The AAFCO Definitions of ingredients are in plain text; my comments are in italics. My comments will make more sense, if you have also read "Tips for Choosing Cat Foods" and "Understanding Cat Food Labels."
Premium Supermarket Brand Chicken and Rice Formula
- Chicken: the clean combination of flesh and skin with or without accompanying bone, derived from the parts or whole carcasses of chicken or a combination thereof, exclusive of feathers, heads, feet, and entrails.
Pretty straight-forward here, and an ingredient I would expect to find in a premium quality cat food. Keep in mind, though, that the amount of bone and/or skin may play a part in the quality of the protein.
- Brewers Rice: the dried extracted residue of rice resulting from the manufacture of wort (liquid portion of malted grain) or beer and may contain pulverized dried spent hops in an amount not to exceed 3 percent
That's "brewers" as in "beer," and may not be the same quality of carbohydrate as ground whole rice.
- Corn Gluten Meal: the dried residue from corn after the removal of the larger part of the starch and germ, and the separation of the bran by the process employed in the wet milling manufacture of corn starch or syrup, or by enzymatic treatment of the endosperm.
This is a real mouthful to digest, both literally and figuratively. Corn is a popular filler, as it is cheap. It is also one of those products that often cause allergies in cats. If I had to choose a product containing corn, I'd probably go for corn meal, which also includes the germ.
- Poultry By-Product Meal: consists of the ground, rendered, clean parts of the carcass of slaughtered poultry, such as necks, feet, undeveloped eggs, intestines, exclusive of feathers, except in such amounts as might occur unavoidably in good processing practices.
I have a problem with by-product meal. While it is true that cats do eat those parts of the poultry (I'll assume chicken and turkey, for want of a better definition) "in their natural (wild) state," the "rendered" part sends cold chills down my spine. In canned foods, once in awhile, you'll see by-products which specifically state organ meats. I might make an exception in that case, but not here.
- Wheat Flour: wheat flour together with fine particles of wheat bran, wheat germ and the offal from the "tail of the mill". This product must be obtained in the usual process of commercial milling and must not contain more than 1.5 percent crude fiber.
Okay, I'll accept that cats may get a small amount of grain in their natural diet - primarily the stomach content of mice or poultry. I won't even touch the term, "offal."
- Beef Tallow: Beef Tallow is obtained from the tissue of cattle in the commercial process of rendering.
Aside from the "rendering," beef tallow is an inferior source of fat for cat food. It is a saturated fat, is low in linoleic acid, and is primarily added for flavor.
- ..preserved with Mixed-Tocopherols (source of Vitamin E): (This is the second part of the "Beef Tallow" mention above). Although I cannot find the AAFCO definition for this preservative, most premium foods now use mixed tocopherols as well as Vitamin A as preservatives. They are not quite as effective as the old chemical preservatives BHA/BTA, so it is important to always check the maximum shelf life date on the label.
- Whole Grain Corn: AAFCO definition is unavailable, but I would assume it is self-explanatory. See my other comments on corn, above.
Continued list of ingredients for the Premium Supermarket Brand Chicken and Rice Formula dry cat food. To review from here, the first listed ingredients were: Chicken, brewers rice, corn gluten meal, poultry by-product meal, wheat flour, beef tallow preserved with mixed-tocopherols (source of Vitamin E), and whole grain corn, in that order. Here are the rest (again, my comments are in italics):
- Sodium Caseinate: UTL on an AAFCO definition. As nearly as I can determine, caseinate (AKA "casein" is a milk product similar to whey, and the sodium is more-or-less self-explanatory.
- Fish Meal: The clean, dried, ground tissue of undecomposed whole fish or fish cuttings, either or both, with or without the extraction of part of the oil. It must contain not more than 10% moisture. If it contains more than 3% salt (NaCl), the amount of salt must constitute a part of the product name, provided that in no case must the salt content of this product exceed 7%.
The only real concern I'd have with this ingredient is the salt content. But the 3% indicated is part of this ingredient only, not the entire product.
- Egg Product: Eggs that are dehydrated, liquid, or frozen, and labeled as per USDA regulations governing eggs. They must be free of shells.
- Potassium Chloride: Potassium salt of hydrochloric acid generally expressed as KCI.Potassium is essential to all species for heart and nerve function.
- Phosphoric Acid: A mineral supplement, consisting of 32% phosphorus
- Brewers Dried Yeast: "One of the best sources of vitamin B. it aids in the repelling of fleas. A probiotic, It also helps reduce stress and reduces sickness" (From DoberDogs.com) Also see this USDA PDF file for more information on Brewers Yeast.
- Natural Flavors: Huh? Actually, the AAFCO does have a new definition of "Natural": A feed or ingredient derived solely from plant, animal or mined sources, either in its unprocessed state or having been subject to physical processing, heat processing, rendering, purification, extraction, hydrolysis, enzymolysis or fermentation, but not having been produced by or subject to a chemically synthetic process and not containing any additives or processing aids that are chemically synthetic except in amounts as might occur unavoidably in good manufacturing practices. But this listed ingredient is so illusive, that it might as well be left out. As a nutrient, it's value is close to nil.
The remaining ingredients are vitamins and minerals, and I won't use the space to define each and every one. They are fairly common to all cat foods, and each serves its own special purpose. For drill, they are calcium carbonate, tetra sodium pyrophosphate, L-Lysine monohydrochloride, salt, choline chloride, vitamin supplements (E, A, B-12, D-3), taurine, zinc sulfate, ferrous sulfate, ascorbic acid (source of Vitamin C), L-Alanine, riboflavin supplement, niacin, calcium pantothenate, manganese sulfate, biotin, thiamine mononitrate, folic acid, copper sulfate, pyridoxine hydrochloride, citric acid, menadione sodium bisulfite complex (source of Vitamin K activity), calcium iodate, sodium selenite.A-4623. A new Cat Food Definitions Glossary will eventually describe them in some detail.
If I had to, I'd personally qualify this brand as "Medium to Good," and I'd use it if I had a large number of cats to feed, if my cats went on a hunger strike and it was the only food they'd eat, or if circumstance prevented me from getting to my nearest pet food store. It would definitely not be among my first choices for day-to-day use for my cats.
Disclaimer: I am not a nutritionist, and the opinions expressed here are my own, as a result of years of personal research of cat foods. I urge my readers to do their own research to form educated opinions. In questions of your own cat's health, you should work in partnership with your veterinarian, who is familiar with your cat's physical condition and history.