Meat by-products in dog food are the non-muscle parts of slaughtered animals: organs, bones, blood, and other tissues left over after the cuts of meat intended for human consumption are removed. Despite their unappealing name, these parts often carry significant nutritional value and are a standard protein source across commercial pet foods.
What Counts as a Meat By-Product
The Association of American Feed Control Officials (AAFCO), the organization that sets pet food ingredient definitions in the U.S., defines meat by-products as “the non-rendered, clean parts, other than meat, derived from slaughtered mammals.” The specific parts included are 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.
When you see “poultry by-products” on a label, the list of parts is similar but specific to birds: hearts, livers, gizzards, lungs, crops, and intestines. These internal organs typically make up 5 to 6 percent of a chicken’s live weight. The key distinction across all by-product definitions is that these ingredients are the parts surrounding the muscle meat, not the skeletal muscle itself.
By-Products vs. By-Product Meal
There’s an important difference between “meat by-products” and “meat by-product meal” on an ingredient list. Plain by-products are raw, wet tissues. By-product meal has been rendered, a process that uses heat and pressure to cook off moisture and fat, leaving a dry, concentrated protein powder. Rendering typically occurs at temperatures around 140°C (284°F) for roughly 45 minutes, which eliminates bacteria and produces a shelf-stable ingredient that’s easier to mix into kibble.
Because meal has had its water removed, it’s actually more protein-dense by weight than raw by-products. When you see “chicken by-product meal” listed high on an ingredient panel, the food contains a meaningful amount of concentrated animal protein.
How Well Dogs Digest Them
One of the most common concerns about by-products is whether dogs can actually use the nutrients in them. Research on beagle dogs fed diets containing animal by-product meal found protein digestibility ranging from 92.8 to 95.1 percent, and fat digestibility between 98.3 and 99.0 percent. Those are high numbers. For context, a protein digestibility above 90 percent is considered excellent for commercial dog food. The particle size of the ground meal (coarse, fine, or very fine) made no statistically significant difference in how well the dogs absorbed either protein or fat.
Nutritional Value of Organ Meats
The word “by-product” sounds like waste, but many of these tissues are nutritionally dense in ways that muscle meat is not. Liver is one of the richest natural sources of vitamin A, iron, and B vitamins. Kidneys provide high concentrations of B12 and selenium. Bone and cartilage contribute calcium, phosphorus, and connective tissue compounds. Cartilage in particular contains glucosamine, a molecule that makes up 30 to 50 percent of the volume of joint cartilage and is commonly sold as a joint supplement for dogs.
In many cultures, organ meats are prized human food. The instinct to view them as inferior comes more from Western grocery store norms than from any nutritional reality. Wild canines eat organs first when they catch prey, precisely because these tissues are so nutrient-rich.
What “Meat By-Products” Doesn’t Tell You
One limitation of the term is vagueness. A label that simply says “meat by-products” without specifying a species (chicken, beef, lamb) can legally come from any slaughtered mammal. If the label says “chicken by-products” or “beef by-products,” the species is locked in. When a manufacturer uses the generic term, you have less visibility into exactly what your dog is eating, which can matter if your dog has a known protein allergy or sensitivity.
The ratio of organs to bone to fatty tissue can also shift from batch to batch. Two bags of food listing the same generic by-product ingredient might contain different proportions of liver versus lung versus bone. Named species and named organs (like “chicken liver”) give you the most consistency.
Safety and the 4-D Question
A persistent concern is whether by-products come from animals that were dead, dying, diseased, or disabled before slaughter, sometimes called “4-D” animals. The reality is more layered than the fear suggests. Animals slaughtered at USDA-inspected facilities for human consumption go through federal inspection, and diseased or disabled animals are not allowed into those plants in the first place. The by-products from these facilities are the same organs and tissues from the same inspected animals that provide steaks and chicken breasts for people.
Under broader feed-grade definitions, certain carcasses or parts rejected from human use can enter the animal feed supply. AAFCO considers these materials adulterated unless they are processed through rendering or high-temperature treatment that eliminates disease-causing organisms. Raw materials from diseased or disabled animals are prohibited from use in raw pet food. To guard against transmissible diseases like mad cow disease, specific high-risk tissues are banned from all animal feed regardless of processing.
Most commercial dog food undergoes heat treatment during manufacturing that provides an additional layer of pathogen elimination beyond any processing the ingredients received beforehand.
How to Read the Label
If you’re evaluating a dog food that contains by-products, a few details on the label can tell you a lot about quality:
- Named species are better than generic terms. “Chicken by-products” tells you more than “meat by-products” or “animal by-products.”
- Named organs are the most specific. “Chicken liver” or “beef heart” on an ingredient list means a single, identifiable tissue rather than a variable mix.
- Meal vs. fresh matters for placement. Ingredients are listed by weight before processing. Raw by-products contain a lot of water, so they may appear higher on the list than their dry-weight contribution warrants. By-product meal, already dried, gives a more accurate picture of how much protein it’s actually contributing.
- Position on the list matters. Ingredients are listed in descending order of weight. A by-product listed first or second is a primary protein source. One listed eighth or ninth is a minor addition.
By-products are not inherently good or bad. A food built around identified organ meats from named species can deliver excellent nutrition. A food using unspecified by-products with no transparency about sourcing gives you less to work with when making informed choices for your dog.