The short answer
By-products are organ meats and other nutrient-rich animal parts that humans in Western countries don't typically eat (think liver, kidneys, lungs, and spleen). They are not hooves, hair, horns, teeth, or floor sweepings. Board-certified veterinary nutritionists generally consider named by-products (like "chicken by-product meal") to be nutritious and well-suited for dogs and cats.
The stigma around by-products is one of the most persistent myths in pet nutrition. It was largely created by marketing, not science. Here's what the evidence actually says.
What by-products actually are
According to AAFCO's official definitions, "poultry by-products" include the non-rendered clean parts of slaughtered poultry such as heads, feet, and viscera (internal organs). "Poultry by-product meal" is the ground, rendered product from poultry by-products. Both terms have strict definitions about what is and isn't included.
In practice, named by-products like "chicken by-product meal" primarily consist of:
- Liver: one of the most nutrient-dense foods on the planet, packed with vitamin A, iron, B vitamins, and copper.
- Kidneys: rich in protein and B12, with a highly digestible amino acid profile.
- Heart: an excellent source of taurine, CoQ10, and lean protein.
- Lungs and spleen: protein-rich organs that contribute to a complete amino acid profile.
- Gizzards and necks: provide protein, collagen, and minerals including calcium and phosphorus.
By AAFCO definition, by-products explicitly do not include feathers, hooves, horns, hair, hide, manure, or stomach/intestinal contents. Those materials are not permitted under the by-product definition.
In many countries around the world, organ meats are considered delicacies. Liver pate in France, haggis in Scotland, anticuchos in Peru. Humans have prized organ meats for centuries. The "by-product" stigma is largely a Western marketing phenomenon, not a nutritional reality.
Why the bad reputation
The anti-by-product movement gained serious traction in the early 2010s as pet food marketing shifted toward humanization, the idea that pet food should look and sound like human food. Brands discovered they could charge premium prices by positioning "no by-products" as a mark of quality, even though there's no nutritional basis for this claim.
The marketing playbook was simple and effective: imply that by-products are "waste" or "filler," then position your product as better because it doesn't contain them. This messaging resonated with consumers who naturally want the best for their pets, but it was driven by marketing strategy, not veterinary science.
The irony is that many "premium" by-product-free foods replaced highly digestible organ meats with lower-quality carbohydrate sources or plant-based protein concentrates, ingredients that dogs and cats are less evolved to utilize.
What WSAVA-aligned veterinary nutritionists say
The professional consensus among board-certified veterinary nutritionists (DACVNs) is clear: named by-products from identified species are quality protein sources. The key word is "named," meaning the species is identified on the label.
Here's what experts at leading veterinary nutrition programs have stated:
- Tufts University Petfoodology: "By-products get a bad rap, but they can provide important nutrients. Organ meats like liver and kidney are far more nutrient-dense than skeletal muscle meat."
- WSAVA guidelines: do not list by-product avoidance as a criterion for selecting good pet food. Their focus is on manufacturer practices: employing nutritionists, conducting feeding trials, and publishing data.
- Clinical nutrition perspective: many veterinary therapeutic diets (prescribed for specific medical conditions) contain by-products because of their nutritional density and digestibility.
Generic by-products are a different story. Unnamed sources like "animal by-product meal" or "meat by-products" (without specifying the species) lack traceability and should be viewed with more caution. You can't identify the protein source, which makes it impossible to manage food sensitivities or ensure consistent quality. Always look for named by-products: "chicken by-product meal," "turkey by-products," etc.
When to avoid by-products
The only well-supported reason to avoid a specific by-product is if your pet has a confirmed allergy or sensitivity to that protein source. If your dog is allergic to chicken, you'd avoid all chicken-derived ingredients, including chicken by-product meal. But you wouldn't need to avoid turkey by-products or beef by-products.
Confirmed food allergies require a veterinary elimination diet trial, typically 8 to 12 weeks of feeding a novel protein or hydrolyzed protein diet under veterinary supervision. Over-the-counter "allergy tests" (blood tests, saliva tests, hair tests) have not been validated for diagnosing food allergies in pets and frequently produce inaccurate results.
If your pet doesn't have a diagnosed protein sensitivity, there's no evidence-based reason to avoid named by-products.
Judge a food by its total nutrition profile, not by whether it contains by-products.
The bottom line
By-products are organ meats: nutrient-dense, highly digestible, and well-suited for dogs and cats. The stigma against them was manufactured by marketing teams, not veterinary nutritionists. Named by-products from identified species (like "chicken by-product meal") are considered quality ingredients by WSAVA-aligned professionals.
The real red flags in pet food aren't by-products. They're unnamed ingredient sources, companies that don't employ board-certified nutritionists, and brands that rely solely on marketing narratives instead of published nutritional data.
Named by-products (like "chicken by-product meal") are organ meats: nutrient-dense and veterinary-approved. The anti-by-product movement was driven by marketing, not science. Avoid unnamed/generic by-products for traceability reasons, but don't let label stigma override nutritional evidence. Focus on the overall quality of the food, not the presence or absence of a single ingredient category.
Sources & Further Reading
- AAFCO. "Official Publication: Ingredient Definitions." 2024.
- Freeman, L.M. "Why You Shouldn't Judge a Pet Food by Its Ingredient List." Tufts Petfoodology Blog.
- WSAVA Global Nutrition Committee. "Guidelines on Selecting Pet Foods." 2021.
- Laflamme, D.P. et al. "Pet Feeding Practices of Dog and Cat Owners in the United States and Australia." JAVMA, 2008.
Based on published veterinary nutrition research (WSAVA, AAFCO, Tufts Petfoodology)
KibbleLab Explains articles are educational, and are not veterinary advice. Before starting an elimination diet, a weight plan, or any major diet change, talk to your veterinarian.
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