Meat by-products in cat food are organ tissues, bones, and other parts of slaughtered animals that aren’t sold as conventional meat cuts for humans. This includes things like liver, kidneys, lungs, spleen, blood, bone, stomachs, and intestines. Despite their unappetizing reputation, many of these parts are nutrient-dense and naturally part of a cat’s ancestral diet. A wild cat eating a mouse consumes the whole animal, organs and all.
What the Label Actually Means
The term “meat by-products” has a specific legal definition set by the Association of American Feed Control Officials (AAFCO), which standardizes pet food labeling in the U.S. It covers the non-rendered, clean parts of slaughtered mammals other than skeletal muscle meat. The official list includes lungs, spleen, kidneys, brain, liver, blood, bone, partially defatted fatty tissue, and stomachs and intestines that have been emptied of their contents. Hair, horns, teeth, and hooves are explicitly excluded.
“Poultry by-products” follows a similar pattern: heads, feet, necks, intestines, and undeveloped eggs from slaughtered poultry. Feathers and litter are not allowed.
One important detail: when a label says just “meat by-products” without naming the animal, it can come from any slaughtered mammal, typically cattle, pigs, sheep, or goats. If the label says “chicken by-products” or “beef by-products,” the ingredient must come from that specific animal. A named species on the label gives you more certainty about what’s in the can.
By-Products vs. By-Product Meal
You’ll see two related but different terms on cat food labels, and the distinction matters. “Meat by-products” refers to fresh, non-rendered parts that still contain their natural moisture. “Meat by-product meal” has been through rendering, a cooking process that removes water and fat, leaving a concentrated dry protein powder. Meal is what you’ll typically find in dry kibble, while wet cat food more commonly uses non-rendered by-products.
The rendering process uses high temperatures to break down tissues, separate fat from protein and bone, and kill any pathogens. This makes the ingredient shelf-stable and safe from a food safety standpoint. However, research has shown that excessive heat during rendering can damage proteins and reduce their digestibility. The quality of a by-product meal depends heavily on how carefully the manufacturer controls time and temperature during processing.
Nutritional Value for Cats
The assumption that by-products are nutritional junk doesn’t hold up. Liver is one of the most nutrient-dense foods that exists, packed with vitamin A, iron, and B vitamins. Kidneys provide high-quality protein. Bone supplies calcium and phosphorus. These are exactly the nutrients cats need as obligate carnivores, and they’re the same organs a cat would eat first after catching prey.
That said, not all by-products are created equal. A by-product blend heavy in liver and kidneys delivers more usable nutrition than one dominated by lungs and connective tissue. Digestibility studies illustrate this range clearly. Research on meat by-product meals found that protein digestibility ranged from about 73% to 79%, while poultry by-product meals performed better at 80% to 89%. For context, these numbers overlap significantly with many standard meat meals. The wide range reflects differences in which specific parts are used and how they’re processed, not an inherent flaw in by-products as a category.
By-products make up a substantial portion of commercial pet food overall. Globally, animal by-products constitute about 32% of dry pet food by mass, making them the single largest animal-derived ingredient category in the industry.
The Safety Question
The bigger concern people have isn’t nutrition but sourcing. By-products must come from animals that were slaughtered, meaning they passed inspection at a processing facility. The AAFCO definition specifies “clean parts” from “slaughtered” animals, which in principle excludes animals that died from disease or unknown causes outside a slaughter facility.
In practice, enforcement has occasionally fallen short. In 2018, the FDA flagged pentobarbital contamination in certain canned dog foods made by The J.M. Smucker Company, including Gravy Train and Kibbles ‘N Bits brands. Pentobarbital is a drug used to euthanize animals, and its presence suggested that euthanized animals had entered the supply chain through rendered fat (tallow). The FDA stated that pentobarbital is illegal in pet food at any amount, and the company withdrew all affected products manufactured from 2016 onward. The FDA noted the levels detected were unlikely to pose a health risk, but the incident exposed a real gap in ingredient traceability.
This contamination was found in a rendered fat ingredient, not in by-products from a named species. That’s one practical reason why pet food experts often recommend choosing products that name specific animals on the label (“chicken by-products”) rather than using generic terms (“meat by-products” or “animal fat”). A named species is easier to trace back through the supply chain.
How to Read the Label
A few guidelines help you evaluate by-products on any cat food label:
- Named species are better than generic terms. “Chicken by-products” tells you more than “meat by-products” or “poultry by-products.” It narrows the sourcing and makes quality control simpler for the manufacturer.
- Position on the ingredient list matters. Ingredients are listed by weight before processing. A by-product listed first contributes more to the food than one listed fifth.
- Meal vs. fresh affects the math. Because by-product meal has had its water removed, it’s a more concentrated protein source by weight than fresh by-products. A food listing “chicken by-product meal” as the second ingredient may actually contain more animal protein than one listing “chicken” first, since fresh chicken is roughly 70% water.
The Environmental Angle
By-products exist because humans eat muscle meat and leave the rest. Using those leftover parts in pet food keeps millions of tonnes of animal tissue out of landfills each year. About 25 million tonnes of animal by-products are rendered annually in the U.S. alone. Without that market, the waste burden from livestock production would be enormous.
The environmental picture isn’t entirely guilt-free, though. A global analysis found that pet food production accounts for 56 to 151 million tonnes of CO2-equivalent emissions per year, or roughly 1% to 3% of total agricultural emissions. By-products carry a lower environmental footprint per kilogram than prime cuts of meat, but they aren’t zero-impact. The revenue they generate for slaughterhouses provides a financial incentive that supports livestock production overall, which means pet food demand is part of the larger agricultural footprint, not separate from it.