Meat by-products are the non-muscle parts of slaughtered animals used as ingredients in pet food. This includes organs like liver, kidneys, lungs, spleen, and brain, along with blood, bone, intestines, and stomachs. It does not include hair, horns, hooves, teeth, or hide trimmings. If you’ve spotted this term on a bag of dog or cat food and wondered whether it’s something questionable, the short answer is that it refers to parts most Americans don’t eat but that are nutritionally dense and widely consumed in other food cultures around the world.
What Parts Are Included and Excluded
The Association of American Feed Control Officials (AAFCO), which sets the standard definitions for pet food ingredients in the United States, defines meat by-products as “the non-rendered, clean parts, other than meat, derived from slaughtered mammals.” The word “meat” in regulatory terms refers specifically to muscle tissue, so by-products are essentially everything else from the carcass that’s clean and edible.
The included parts are: lungs, spleen, kidneys, brain, liver, blood, bone, partially defatted fatty tissue, and stomachs and intestines that have been emptied of their contents. The excluded parts are hair, hooves, horns, teeth, hide trimmings, manure, intestinal contents, and floor sweepings or other non-carcass material. According to Tufts University’s veterinary nutrition service, the regulatory definition is quite specific about keeping out the parts people typically imagine when they hear “by-products.”
How By-Products Differ From Meat and Meat Meal
Pet food labels use several related terms that sound similar but mean different things. “Meat” on a label refers to muscle tissue, including the muscle from the tongue, diaphragm, heart, and esophagus. “Meat by-products” are the raw, non-rendered organ and bone parts described above. “Meat meal” and “meat by-product meal” are versions of these ingredients that have been rendered, a cooking process that removes moisture and fat to create a dry, concentrated protein powder.
Many pet food manufacturers use rendered by-products in meal form because raw organs and bones are difficult to store and handle in a factory setting. So if you see “chicken by-product meal” instead of “chicken by-products,” the underlying animal parts are similar, but the meal version has been heat-processed and dried. AAFCO requires different names on the label to reflect whether the ingredient is raw or rendered.
Labels must also name the specific animal species the by-products come from, with one exception: if the source is cattle, swine, sheep, or goats, the label can simply say “meat by-products” without specifying which of those four animals it is.
Nutritional Value of Organ-Based Ingredients
The negative reputation of by-products comes largely from the unappealing mental image of organs and bones rather than from their actual nutritional profile. Liver is one of the most nutrient-dense foods in nature, packed with vitamin A, iron, and B vitamins. Kidneys are rich in protein and minerals. Bone provides calcium and phosphorus. These are parts that wild canines and felines consume first when they catch prey, and they remain staple foods for humans in many countries.
A 2023 study published in the journal Life tested diets made with animal by-products on beagle dogs and found protein digestibility between 92.8% and 95.1%. The European Pet Food Industry Federation considers 80% to be the normal digestibility benchmark, so the by-product-based diets in that study exceeded the standard by a wide margin. Fat digestibility was even higher, ranging from 98.3% to 99.0%. In practical terms, this means the dogs’ bodies were absorbing nearly all of the protein and fat from these ingredients.
How By-Products Are Processed
Raw by-products collected from slaughterhouses go through a process called rendering before they end up in most dry pet foods. The raw material is first ground into smaller pieces, then heated to separate fat from protein and moisture. The fat gets skimmed off and purified, while the remaining solids are dried into a concentrated protein meal.
There are two main approaches. Wet rendering cooks the material in water or steam at around 90 to 95 degrees Celsius and is typically used for fattier tissues, producing higher-quality fats. Dry rendering heats the material without added water in closed vessels at 115 to 135 degrees Celsius and is more common for bones and high-protein materials. Modern continuous rendering systems feed material through a series of heated chambers at those same temperatures, making the process faster and more consistent. The end result in all cases is a shelf-stable ingredient that can be mixed into kibble or canned food.
Why the Term Sounds Worse Than It Is
Pet food marketing has created a hierarchy where “real chicken” sounds premium and “chicken by-products” sounds cheap or unsafe. In reality, a chicken liver is no less “real” than a chicken breast. The distinction is cultural, not nutritional. Organ meats provide nutrients that muscle meat alone cannot, which is why many veterinary nutritionists consider by-products a valuable part of a balanced pet diet rather than a filler or inferior substitute.
The quality of by-products does vary between manufacturers, just as the quality of any ingredient varies. A pet food company sourcing fresh organs from inspected slaughterhouses produces a different product than one using lower-grade rendered material. The ingredient name on the label tells you what category of animal parts went into the food, but it doesn’t tell you how fresh or carefully handled those parts were. That distinction comes down to the manufacturer’s sourcing standards, which is why the brand and its reputation matter more than whether the label says “meat” or “meat by-products.”