Labels & Ingredients

What Actually Counts as a "By-Product" in Pet Food

Updated July 28, 2026

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By Morgan Reyes

The Short Answer

There is no single AAFCO definition of "by-product." There are five separately-defined ingredients that use the word, each with its own text and its own exclusion list, and those lists do not match each other.

The two non-rendered ones must come from slaughtered animals. The rendered ones ("meal") are cooked under heat and pressure to kill bacteria and then ground. Each definition excludes different things: teeth are named only in the mammal by-products definition, hide trimmings and manure only in the rendered ones.

And the word itself predicts nothing about quality in either direction. A bag listing by-products may be excellent. A bag advertising none of them may contain the same material under prettier names.

Which one is actually on my bag?

Match the exact phrase on your label before reading any definitions, because they are not interchangeable.

Two things to notice straight away. "Meat meal" and "meat and bone meal" do not have the word "by-product" in them and are by-products anyway, which is the single most common way a reader gets misled by a label. And there is a species rule: unless the material comes from cattle, pigs, sheep or goats, AAFCO requires the species to be named. That is why you see "venison by-products" rather than a bare "by-products."

The definitions, word for word, and exactly what each one excludes

These are quoted from AAFCO's own ingredients-list page, fetched 28 July 2026. Where a qualifying clause matters, it is included, because leaving it off changes what the rule permits.

Meat by-products:

"the non-rendered, clean parts, other than meat, derived from slaughtered mammals. It includes, but is not limited to, lungs, spleen, kidneys, brain, livers, blood, bone, partially de-fatted low temperature fatty tissue and stomachs and intestines freed of their contents. It does not include hair, horns, teeth and hoofs. It shall be suitable for use in animal feed. If it bears a name descriptive of its kind, it must correspond thereto."

That bolded sentence is the most useful line in the whole definition and it is almost never quoted. The exclusion list is short and specific: hair, horns, teeth, hoofs. Nothing else.

Poultry by-products:

"non-rendered clean parts of carcasses of slaughtered poultry, such as heads, feet and viscera, free from fecal content and foreign matter except in such trace amounts as might occur unavoidably in good factory practice. If the product bears a name descriptive of its kind, it must correspond thereto."

Note what changes. This one says nothing about hair or horns, which poultry do not have, and instead excludes fecal content and foreign matter. And it permits unavoidable trace amounts. The exclusions are ingredient-specific, not universal, which is the detail that makes most summaries of this topic wrong.

Meat meal:

"rendered product from mammal tissues, exclusive of any added blood, hair, hoof, horn, hide trimmings, manure, stomach and rumen contents except in such amounts as may occur unavoidably in good processing practices. It shall not contain extraneous materials not provided for by this definition. The Calcium (Ca) level shall not exceed the actual level of the Phosphorus by more than 2.2 times. It shall not contain more than 12% Pepsin indigestible residue and not more than 9% of the crude protein in the product shall be Pepsin indigestible."

Longer exclusion list than the non-rendered version, plus hard chemical limits. That calcium-to-phosphorus cap is a real quality control: it stops a manufacturer passing off ground bone as protein.

Meat and bone meal is the same text with "including bone" added, a minimum of 4% phosphorus, and the same 2.2x calcium cap.

Animal by-product meal:

"the rendered product from animal tissues, exclusive of any added hair, hoof, horn, hide trimmings, manure, stomach and rumen contents, except in such amounts as may occur unavoidably in good processing practices. It shall not contain extraneous materials not provided for by this definition. This ingredient definition is intended to cover those individual rendered animal tissues that cannot meet the criteria as set forth elsewhere in this section."

That last sentence is the honest one: this is the catch-all category, for rendered tissue that does not qualify as anything more specific.

Here is what each one actually excludes, side by side:

Teeth appear in exactly one definition. Any page telling you that by-products never contain teeth, hooves and hair as a blanket rule is describing a definition that does not exist.

One gap worth stating rather than papering over: "poultry by-product meal" appears on neither of AAFCO's consumer pages, despite being a common label term. Its definition lives in AAFCO's Official Publication, which is sold rather than published, so this guide does not quote it. An earlier version of this page did quote it, and we cannot verify that text against a public source.

AAFCO's own two pages disagree with each other

This is small, and it is the best evidence that anybody quoting this definition has actually read it.

AAFCO publishes the meat by-products definition on two of its own consumer pages, and the two versions are not identical. Both fetched 28 July 2026:

None of these changes the meaning. That is exactly why it is interesting: it tells you these consumer pages are transcriptions, and the authority sits somewhere else.

That somewhere else is AAFCO's Official Publication, which is purchase-only. So this guide quotes AAFCO's public pages and names which one, rather than claiming to quote the Official Publication. Anyone who tells you they are quoting the OP verbatim, for free, is worth a second look.

What rendering actually is, and why "meal" means ground

Rendering is a cooking process, and its first job is killing bacteria.

In AAFCO's words, rendered products "have been cooked to destroy any harmful bacteria before they are shipped to a pet food manufacturing plant. During rendering, heat and pressure remove most of the water and fat, leaving primarily protein and minerals. The term 'meal' is used because in addition to cooking, the products are ground to form uniform-sized particles."

So "meal" is not a euphemism. It is a particle-size description.

Tufts puts the same thing more plainly: rendering "is the process of cooking an ingredient at high temperatures to separate the fat and protein out. The end product is a dry, high protein powder that is easily stored, transported and incorporated into dry pet foods."

Hold onto the bacteria-killing part. It is what the next section turns on.

Does any of this include diseased or dead animals?

This is the question underneath the whole by-product argument, and it deserves a straight answer rather than a reassuring one. AAFCO answers it in two parts, and the two parts differ.

For plain meat by-products, the answer is no:

"Under the precise definition above, the byproducts must be from 'slaughtered mammals.' The USDA, which oversees the slaughtering of animals for human consumption, would not allow diseased or disabled animals into the plant for processing in the first place."

For the broader group that includes rendered ingredients, the answer is different:

"However, under the broader definition for byproducts, which includes ingredients like meat and bone meal, yes, certain carcasses or parts may be rejected from use for humans and processed into animal feed. Meat and meat byproducts not directly suitable for animal food that are designated as 4-D (dead, dying, diseased or disabled). These are considered adulterated, unless processed in a manner that rids them of disease-causing microorganisms prior to becoming animal feed. This is most often done by rendering, which subjects the materials to heat and pressure to eliminate harmful bacteria."

And on raw food specifically: raw materials that may have come from diseased or disabled animals are prohibited from raw pet food.

So the honest summary is three sentences, not one. A label reading "meat by-products" requires slaughtered animals, and 4-D material is not permitted in it. A label reading "meat and bone meal" or "animal by-product meal" sits under the broader umbrella where rejected material may enter, is legally adulterated unless processed to eliminate pathogens, and in practice is rendered precisely to do that. And raw pet food is held to the stricter rule.

That is neither the reassurance the industry offers nor the horror story the marketing implies. It is the reason the rendered-versus-non-rendered distinction is worth learning, and it is the one thing most pages on this topic set up and then never use.

Why the word got its reputation

The reason is not what we previously told you on this page, and the correction matters enough to make out loud.

An earlier version of this guide said Tufts' own read was that the reputation is "largely a competitive marketing effect." Tufts says no such thing, and attributing it to them was our error. What Tufts' veterinary nutrition service actually names is two things.

Internet horror stories. "While the internet is full of horror stories about what is supposedly in by-products, there are actually strict legal definitions of what can be included under this term."

Rendering variability, which you cannot check. "Like all ingredients, rendered meals can vary from quite nutritious to poor quality, and there is no way to assess ingredient quality from the label or the website."

Tufts does make a marketing point, and it is sharper than the one we had put in their mouths:

"Interestingly enough, a number of companies use organ meats and other ingredients that fit within the definitions of by-products in their foods, but to avoid the stigma of 'by-product' list them as liver, heart, kidney, plasma, etc. Some of these companies even then advertise that they do not contain by-product. Don't be fooled by a by-product by a different name."

That is a re-usable label-reading skill, which "the reputation is a marketing effect" was not.

Now the part we owe you about our own source. This page's nutritional argument rests substantially on that one Tufts post, and that post carries a disclosure block naming its authors' industry funding. Verbatim, Dr Freeman "has received research or residency funding from, given sponsored lectures for, or provided professional services for AKC Canine Health Foundation, Aratana Therapeutics, Elanco, Guiding Stars Licensing Co LLC, Hill's Pet Nutrition, Morris Animal Foundation, Nestlé Purina PetCare, P&G Petcare (now Mars), and Royal Canin." Dr Heinze and Dr Linder disclose comparable relationships, including with Purina, Royal Canin, Hill's and Virbac.

We are still citing it, and here is the reasoning. It is a reasoned piece from a credible academic nutrition service, the nutrient-density claim is independently sensible, and the definitions in this guide come from AAFCO rather than from Tufts. But a page arguing that you should be sceptical of pet-food marketing, resting on authors funded by the largest pet-food manufacturers, has to say so. Tufts disclosed it. Passing that on is the minimum.

The argument nobody makes: food waste

Here is a framing that almost never appears in this debate, from the same Tufts piece:

"Think about all the cows, pigs and chickens that are slaughtered every day... what would we do with all those healthy organs and other bits that we don't want to eat if we didn't feed them to our pets who appreciate them? Feeding these foods to pets not only is safe and healthy, but it is better for the environment and dramatically reduces food waste."

Whatever you conclude about ingredient quality, that is the actual alternative. A pet-food industry that used only muscle meat would need more slaughtered animals to feed the same number of pets, and the organs would go somewhere else or nowhere.

Did the new label rules change any of this?

No, and the dates are worth getting right because this gets reported as current news.

AAFCO membership approved new model regulations for pet food on 31 July 2023. They were published in the 2024 Official Publication, and AAFCO recommends states use enforcement discretion for six years from that publication, which puts full transition around 2030. So both old and new labels are legitimately on shelves right now.

What changes: a Pet Nutrition Facts box replacing the guaranteed analysis, an intended-use statement on the front panel, and clearer handling of vitamin names in the ingredient list.

What does not change: by-product naming and the by-product ingredient definitions. Everything quoted on this page survives the transition unchanged.

Bottom line: "by-product" is five different legal definitions wearing one word, and the exclusions differ between them, so any blanket claim about what by-products do or don't contain is describing a rule that does not exist. The non-rendered ones require slaughtered animals and cannot legally contain 4-D material; the rendered ones sit under a broader umbrella where rejected material may enter and must be processed to eliminate pathogens. None of that tells you whether a given food is good, because ingredient quality is not visible on a label at all. Read the bag for species, life stage and the complete-and-balanced statement, and treat "no by-products" as a marketing decision rather than a nutritional one.

FAQ

Are by-products safe for pets?

The definitions carry a safety requirement of their own. AAFCO's meat by-products definition states "It shall be suitable for use in animal feed," and rendered products are "cooked to destroy any harmful bacteria" before they reach a pet food plant.

On nutrition, Tufts states that by-products, mainly organ meats and entrails, "often provide more nutrients than muscle meats on a per-weight basis."

What the word cannot tell you is quality. That is not a hedge, it is Tufts' own position: there is "no way to assess ingredient quality from the label or the website."

Do by-products contain diseased or dead animals?

It depends on which ingredient, and the honest answer has two halves. See the section above for AAFCO's wording in full.

Is there a single AAFCO definition of "by-product"?

Not as an ingredient. There are five separately-defined ingredients, each with its own text.

AAFCO does define the general term, as "secondary products produced in addition to the principal product," and notes that rendered ingredients like meat and bone meal are therefore also by-products. So the word has a general definition and the ingredient does not, which is why arguing about "by-products" as a single thing goes nowhere.

Does "no by-products" on a bag mean anything?

Less than it looks. Some companies use ingredients that fit the by-product definitions, list them as liver, heart or kidney, and then advertise that the food contains no by-products. Tufts' line is the one to remember: "Don't be fooled by a by-product by a different name."

Is "human grade" a real standard or just marketing?

Real, and voluntary. AAFCO publishes a human-grade standard with guidelines and a compliance checklist, dated 2023, and the claim requires manufacture under regulations for human-edible food.

That is a genuine requirement, unlike "by-product-free," which has no definition behind it. It also says nothing about whether the food is nutritionally better, and nothing about by-products.

What does AAFCO actually have the power to do?

AAFCO is an association of state and federal feed control officials. It writes model definitions and model regulations; individual states adopt them into their own feed law, and state officials enforce them. So the definitions on this page have legal force through state law rather than through AAFCO itself.

Keep reading

• Read Any Pet Food Label in 60 Seconds. The procedure this guide's definitions plug into, in the order to check things.
• Grain-Free Dog Food: What the Science Actually Says. Where ingredient position on the label genuinely does matter, and why.

Two more are coming and are not linked because they do not exist yet: a term-by-term guide to which label phrases have legal definitions ("natural," "premium," "holistic"), and a dry-matter calculator for comparing two bags honestly.

A Note on Scope

This guide explains ingredient definitions. It is not veterinary advice, and no veterinarian reviewed it. It cannot tell you which food is right for your animal, and it deliberately does not recommend one. If your pet has a diagnosed condition, a food allergy, or is losing or gaining weight unexpectedly, that is a conversation with your vet rather than a label-reading exercise.

Sources

• AAFCO, what's in the ingredients list. Fetched 28 July 2026. Source for every ingredient definition quoted above and for the rendering description. Does not contain a definition of poultry by-product meal.
• AAFCO, frequently asked questions. Fetched 28 July 2026. The 4-D answer, the general definition of "byproducts," the species-identification rule, and the second, slightly different wording of the meat by-products definition.
• AAFCO, on the approval of the new model pet food regulations and the Pet Food Label Modernization overview. The 31 July 2023 approval, the 2024 Official Publication, and the six-year transition.
• Tufts Petfoodology, "Don't be bothered by by-products," 31 May 2016. The nutrient-density claim, the two causes of the ingredient's reputation, the relabelling point and the food-waste argument. Carries an author disclosure block naming funding and paid services from Hill's, Nestlé Purina, Royal Canin, Mars/P&G Petcare, Elanco, Virbac and others, discussed in-body above. Bylined "Clinical Nutrition Team" rather than to the three individuals named in that block.