Say the phrase “meat by-products” out loud in a pet store and watch a stranger’s face change. It’s become shorthand for everything people fear is wrong with commercial pet food — filler, floor sweepings, “the parts they can’t sell.” Search the term online and you’ll find outrage before you find a definition. So let’s start with the actual definition, because the regulatory meaning of “by-products” and the internet’s version of it are two very different things.
What “by-products” actually means
Under the model ingredient definitions published by the Association of American Feed Control Officials (AAFCO) — the body whose definitions most U.S. states adopt into law for how pet food ingredients must be labeled — “meat by-products” are the clean, non-rendered parts of slaughtered mammals other than meat: organs like lungs, spleen, kidneys, liver and blood, explicitly excluding hair, horns, teeth and hooves. “Poultry by-products” follow the same logic for chicken and turkey: necks, feet, undeveloped eggs and viscera, again with specific exclusions written into the definition. None of this is “waste” in the trash sense — it’s tissue from an animal already slaughtered for the human food supply, and some of it, liver especially, is more nutrient-dense than muscle meat, not less.
Myth vs. fact
Myth: “By-products are floor sweepings and waste”
Fact: The AAFCO definition is specific about which organs and tissues qualify, and it explicitly excludes contaminants like hair and horn. A manufacturer listing by-products is using a defined, regulated ingredient category — not an undefined grab-bag. That doesn’t mean sourcing quality never varies between suppliers, but the category itself isn’t the loophole people assume it is.
Myth: “By-products have no nutritional value”
Fact: Organs like liver and kidney are often richer in vitamins, minerals and certain amino acids than skeletal muscle — liver alone is a meaningful natural source of vitamin A, iron and B vitamins. The Nutrient Requirements of Dogs and Cats, published by the National Research Council (NRC) and the scientific basis for AAFCO’s own nutrient profiles, doesn’t treat organ tissue as a lesser ingredient. Wild canids and felines have historically eaten organs right alongside muscle, not as an afterthought.
Myth: “Chicken” will always beat “chicken by-product meal” on a label
Fact: It depends what you’re actually measuring. Whole “chicken” as a first ingredient includes water weight, so once it’s cooked down, its real protein contribution can end up smaller than a rendered meal listed further down the list. “Chicken by-product meal” is already dehydrated and concentrated, meaning more protein per weight of the finished ingredient. Ingredient order reflects weight before cooking, not nutrient density after it — a distinction that trips up even careful label-readers.
Key Takeaways
- By-products are a defined, regulated ingredient category under AAFCO — not an undefined catch-all.
- Organ meats can be more nutrient-dense than muscle meat, not less.
- Ingredient order reflects pre-cooking weight, not nutrient concentration — “chicken” isn’t automatically better than “chicken meal.”
- The real flag is an unnamed species (“meat by-products”), not the word “by-products” itself.
Where the real red flag is
None of this means every use of by-products is equal, and there is one genuine distinction worth watching for: named versus unnamed species. “Chicken by-product meal” tells you exactly what animal it came from. “Meat by-products” or “animal by-products,” with no species named, doesn’t — and that’s a real transparency gap, especially if your dog or cat has a diagnosed food allergy and you need to know precisely which proteins are in the bowl. Sourcing and quality control can also still vary meaningfully between brands even when both use technically legal terminology, which is exactly why a manufacturer’s recall history and general transparency matter as much as any single ingredient name.
How to check a label for yourself
The fastest way through all of this is to stop treating “by-products” as a single verdict and start checking two things instead: is the species named, and does the rest of the ingredient panel and nutritional adequacy statement hold up. The WSAVA Global Nutrition Toolkit specifically encourages pet owners to contact a manufacturer directly with sourcing questions when a specific health condition is in play — a normal, reasonable step, not a sign something’s wrong. Peeku’s scoring engine takes the same approach at the ingredient level: it doesn’t dock a food just for containing a named by-product meal, but it does flag vague, unnamed sourcing and weighs it against everything else in the formula, so you get a fuller picture than a single scary word on the front of the bag.
By-products aren’t the villain the internet has made them out to be, and they aren’t automatically a green light either. The word itself tells you almost nothing on its own — what matters is whether the species is named, how the rest of the formula holds up, and whether the manufacturer is transparent about where its ingredients come from. Read past the word, and the picture gets a lot clearer.