To read about what is in specific byproduct ingredients, read more about rendered products here.

The nature and use of byproducts in pet foods, especially animal-origin byproducts, provoke a wide range of opinions. These opinions often revolve around which ingredients are suitable for humans vs. pets, concerns about disease transmission and health, the economics of food production and personal preference, among other factors.

Based on nutrient content and safety resulting from processes used to produce the byproducts and the animal foods in which they are used, AAFCO’s position is that byproducts can be safely used to provide nutrition for lots of animals.



AAFCO defines byproducts as:

“Secondary products produced in addition to the principal product.”

  • This means byproducts can be secondary products from any primary food product source.
  • There may be more than one byproduct from processing a single food product.

(To learn more about safety and utility, read about ingredient standards.)

Essentially, a byproduct is what is left over after the intended product has been made. In the case of animal feeds, including pet foods, it’s often the excess materials left over after processing human foods.

Many raw commodities, when processed, result in a primary product for human consumption and secondary products mostly (but not exclusively) for animal consumption. Using primary animal and plant products for humans and their related byproduct materials for animals is a common practice.

This doesn’t mean byproducts are unsafe or lack nutrition—they just aren’t part of the original primary products.

For example, the milling of flour results in the production of several byproducts, one of which is wheat bran. Wheat bran is an ingredient in other products for animal and some human consumption. Most Byproducts do not include the word “byproduct” in the ingredient name.

One additional source of confusion for consumers may be use of the phrase “co-product” to describe a secondary product that is a major product of a particular manufacturing process. Co-product is an industry expression. It is not an AAFCO official feed term.


Animal-Sourced Byproducts

The AAFCO Model Regulations for all animal feeds require that the ingredients list include the species of animal that meat and meat byproducts comes from, unless the meat or meat byproducts comes from cattle, swine, sheep or goats.

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 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.

Because it’s difficult to store and handle raw ingredients properly in a pet food manufacturing facility, many pet food plants use rendered byproducts in a meal form. Rendering is a process that cooks an ingredient to prevent microbial contamination. If this is the case, the ingredients listed on the label will have different names because they are rendered rather than raw.

For more about raw pet food, click here.


Personal Choice and Aesthetics

Some arguments about byproducts focus on whether they are appetizing. But AAFCO does not regulate consumers’ opinions regarding ingredient aesthetics.

Instead, AAFCO strives to provide definitions that consumers can count on so they understand what is and is not in such products. This enables consumers to read labels and decide for themselves.



Certain byproducts in the raw, unprocessed state may be adulterated. Such products are of concern because of the potential or actual existence of disease-causing microbial contamination, such as certain types of Salmonella or E. coli.

Heat Treatment

Raw, unprocessed byproducts are prohibited from use in finished animal feed unless the products are heat-treated to kill any microbial contamination. In commercial pet food manufacturing, both canned and kibbled products are heat-treated during manufacturing and packaging. Additionally, many animal protein products are heat-treated at rendering plants and made into dry meals before shipment to a pet food manufacturer.

In any case, correct heat treatment of commercially-manufactured pet foods is commonly practiced to prevent microbial contamination and disease transmission.