By-products in pet food

There isn’t an ingredient that gets more negative attention than by-products. But what are by-products? Do they really include hooves, hair and teeth? Are they poor quality meats?

I’ve collated the most commonly asked questions about by-products here, in a hope to explain some of the misconceptions people have about by-products and sort the fact from fiction.

What are by-products?
The AAFCO definitions are very specific when it comes to by-products, what it includes and doesn’t include. Please note that the terms may differ depending on the country – if you are based in the UK or EU, you may have meat and animal derivatives labelled instead.

Firstly, what does AAFCO define as a by-product?
“Secondary products produced in addition to the principal product.”
This means anything that is produced secondary to the primary product is considered a by-product, so a product such a meat for the human food industry will produce by-products that humans don’t eat that are then set aside for pet food. AAFCO states: “During the slaughter and meat-cutting process, certain carcasses or parts may be rejected for human use and can be expected to be processed into animal feed. This may include meat that doesn’t meet aesthetic standards, or internal organs or other parts that normally aren’t used for human food.”

Meat Byproducts are defined as: “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.”
It’s very important to draw attention to the exclusions under this definition; as hair, horns, teeth and hooves cannot be in this ingredient. Now, the reason the meat isn’t named means that it must come from cattle, sheep, goat or pigs as it follows the AAFCO definition of “meat”. It also means that some pet foods may use a combination of meat sources or change the meat source from time to time.

If the ingredient is categorised as Poultry Byproducts this is defined as: “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.” In poultry by-products you CAN include heads and feet – which in many dog treats you’ll already find these products. But it’s important to note that they must be free of faecal or foreign content.

Now for Animal Byproduct Meal, this is different again! Often people take this ingredient to mean it’s a mixture of ‘unidentifiable meats’ but this actually isn’t the case. Animal by-product meal is defined as: “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. This ingredient is not intended to be used to label a mixture of animal tissue products.” Note that last sentence, animal by-product meal isn’t a combination of meat tissues from multiple different animals, its intended to cover tissues that don’t match the other definitions, usually what isn’t in meat and bone meals.

The final definition is Poultry By-Product Meal: “consist of the ground, rendered, clean parts of the carcass of slaughtered poultry, such as necks, feet, undeveloped eggs and intestines, exclusive of feathers except in such amounts as might occur unavoidably in good processing practices.  The label shall include guarantees for minimum crude protein, minimum crude fat, maximum crude fiber, minimum Phosphorus (P), and minimum and maximum Calcium (C).  The Calcium (Ca) level shall not be more than 2.2 times the actual Phosphorus (P) level.  If the product bears a name descriptive of its kind, it must correspond thereto.” So again, this ingredient also cannot contain feathers, unless a small bit accidentally gets mixed in. Again, necks, feet and eggs are all things you will find in pet foods, particularly DIY foods so there’s still nothing you wouldn’t expect in there.

Do by-products include diseased, dying and decaying meat?
Many owners express concern about dead, decaying or diseased meat (3D) being used in pet food. However, AAFCO states “Meat and meat byproducts from animals that have died by other means than slaughter aren’t directly suitable for animal food because these products are considered adulterated. They can’t be used for animal feed unless they contain no chemical additives and are heat-treated and further processed. For dry kibble and canned pet foods, the final product should be free of disease-causing bacteria.” This means that you cannot use decayed or diseased meat without actually processing it first for it to be considered safe, it also means that the final product must be free from bacteria so it must be tested for safety in the final formulation. This does NOT mean that every by-product or meat based ingredient contains this type of meat, and generally it is safer and cheaper to use quality meat such as internal organs that don’t require further processing to be safely used.

Are by-products low quality meat or low in protein?
Simply, no. By-products are some of the best quality and richest source of protein for pets. In the wild, animals go for the internal organs or “by-products” of their kill and ingest these first as they contain the most protein and energy compared to the rest of the carcass. By-products get their name from their intended use, not because they lack any nutritional value; as their intended use is for pet food, it makes them a ‘by-product’ of the human food chain.

As for protein level, by-product meals are rich in protein. As they have been cooked, dried and ground, the water is mostly removed, creating a concentrated source of protein – it’s essentially a protein powder. The water content of fresh meat means the protein fraction is lower; this also means you would need to feed MORE to get the same level of protein from the same amount of by-product meal which not only is hugely wasteful, it also means that the pet needs to eat more to meet it’s requirements. See the graphic below.

Source: Royal Canin

Should I avoid by-products? I personally don’t see any reason to avoid by-products. There is nothing ‘bad’ about by-products, in fact they provide superior nutrition than muscle meat alone can. I think it’s more important to focus on the diet as a whole, it’s benefits for your pet and its overall formula not just one or two ingredients. Ingredients work synergistically with eachother which is why I recommend not zeroing in on an ingredient list because it doesn’t tell you the whole story. Read more about ingredient lists here.

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AAFCO Talks Pet Food (2021) By-products. Available online at:

Royal Canin – What is the nutritional value of by-products in pet food? Available online at:

2 thoughts on “By-products in pet food

  1. I’ve read that companies do NOT have to list the products that were BROUGHT to the facility but have to list products that were MADE or rendered at the facility. This is the concern, and that the rendered meat brought to the facility is not monitored and this is where the extra stuff is hiding.

    • They have to list everything that is in the food. They do not have to list potential traces, allergens or other things that the food may have been in contact with in the factory (unlike human foods).