Animal by-products in pet food: understanding the difference (and when to avoid them)
"Meat and animal by-products." You read this on millions of pet food bags and cans, and two opposite reactions exist: some owners ignore it entirely, others put the product back on the shelf. Both reactions are too simplistic.
The reality is more nuanced, more interesting, and frankly more useful for choosing quality nutrition for your dog or cat. This guide dismantles the misconceptions in both directions.
What EU and US regulations actually say
In Europe, terminology is governed by Regulation (EC) 767/2009 on the placing on the market and use of pet food. In the US, AAFCO definitions govern ingredient naming on domestic products.
Animal by-products are defined as parts of the animal not intended for human consumption - either because they have no human market, or because they have been excluded from it preventively. The legal definition includes: lungs, spleen, liver, kidneys, stomach, cleaned intestines, feet, heads, stripped carcasses.
Critical note: liver, heart, kidneys and spleen are by-products in the legal EU sense, while they are nutritionally "noble offal" consumed by humans in most world cultures. Legal classification and nutritional quality are not the same thing.
Our how to read a pet food label guide explains in detail how to interpret the regulatory ingredient list.
The distinction that actually matters: named vs unnamed
This is where the real difference lies. It is not "by-product yes/no" but "named by-product or vague."
Named by-products (identified by species): no problem
When you read on a label:
- "Chicken liver"
- "Beef heart"
- "Pork kidney"
- "Lamb lung"
...you know exactly what it is. The species is named, the organ is specified. It is traceable. And critically, these are nutritionally excellent foods.
Liver is one of the most nutrient-dense foods in existence: it contains vitamin A (retinol), the full B complex (B1, B2, B3, B5, B6, B9, B12), highly bioavailable haem iron, zinc, copper, and coenzyme Q10. For cats, liver is a preferred source of retinol - cats cannot convert beta-carotene to vitamin A the way humans and dogs can.
Heart is a muscle (not an organ in the nutritional sense), rich in high-quality proteins, taurine (particularly important for cats who cannot synthesise taurine), and CoQ10. Formulas that list "chicken heart" or "beef heart" near the top demonstrate transparency and nutritional quality superior to many "muscle only" formulas.
Kidneys are rich in protein, B vitamins and selenium. Lungs are a source of protein and glycosaminoglycans (precursors to glucosamine/chondroitin) - their presence in a formula naturally contributes to joint health, even if levels vary.
Summary: named by-products identified by species and organ are valuable ingredients. Dismissing them reflexively is a mistake.
Unnamed by-products (unidentified): justified caution
Conversely, when you read:
- "Meat and animal by-products"
- "Animal derivatives"
- "Animal proteins"
- "Animal fats"
...you know nothing. Not the species (chicken? pork? lamb? horse?), not the organ, not the quality, not the consistency batch to batch.
Why is this problematic?
1. The composition can vary with every manufacturing run. A manufacturer using "meat and animal by-products" can use chicken in one batch, pork in the next, and indeterminate poultry in a third. This is legal. And if your dog develops a food sensitivity, you cannot identify the culprit.
2. The real quality is untraceable. Unidentified by-products allow the use of the least valuable raw materials (feathers, hooves, blood, stomach contents) at maximum legal proportions without revealing this on the label. This is not always the case - some manufacturers use vague terminology for supply chain flexibility while maintaining real quality - but the consumer has no way to verify.
3. FEDIAF and AAFCO permit this opacity. Regulatory bodies require sanitary safety (all ingredients must be of healthy animal origin, traceable at the company level) but do not require consumer transparency on exact composition. This is a regulatory blind spot.
Our worst pet food ingredients guide develops this point with concrete product examples.
The "animal fats" case
The mention "animal fats" deserves its own paragraph. It is the most frequently misunderstood ingredient.
Unspecified animal fats are used as an energy source and flavour carrier (kibbles are often sprayed with them after extrusion). They provide fatty acids, including arachidonic acid (important for cats). Their presence is not intrinsically negative.
The problem, again, is opacity: without species identification, you do not know whether these are chicken fats (relatively favourable omega profile) or low-quality tallow recovered from rendering plants. The impact on the omega-6/omega-3 ratio can be significant. Our omega-3 pet food guide details why the omega-6/omega-3 ratio matters for cardiovascular and inflammatory health in your pet.
Conversely, "chicken fat" or "salmon oil" identified = you know what it is, the profile is known, quality is assessable.
FEDIAF and AAFCO definitions side by side
Terminology varies between Europe and the US, complicating the reading of imported product labels.
| European term (FEDIAF) | US term (AAFCO) | Simplified definition |
|---|---|---|
| Animal by-products | Animal by-products | Non-muscle parts excl. meals, species unnamed |
| Meat and offal | Meat and meat by-products | Includes muscle, species unnamed |
| Chicken liver | Chicken liver | Chicken liver, species named |
| Meat meals | Meat meal | Dried meat and by-products, species sometimes named |
| Animal derivatives | (no US equivalent) | EU only, broadest catch-all term |
| Animal fats | Animal fat | Fats not identified by species |
Full AAFCO definitions are published at aafco.org. FEDIAF regulations are at fediaf.org.
When by-products are a positive signal
There are situations where the presence of named by-products near the top of the ingredient list is a quality signal, not a compromise.
Whole prey formulas
Brands like Orijen and Acana intentionally include liver, kidneys, lungs and spleen in their formulas. These "by-products" are listed individually with species and organ specified. This is precisely what makes them nutritionally superior to "muscle only" formulas: the micronutrient profile of a whole animal is far more complete than that of muscle alone.
The whole prey philosophy is grounded in observations of wild predator behaviour: carnivores preferentially consume organs (liver, heart, kidneys) before muscles, suggesting an instinctively recognised nutritional superiority. Comparative feeding studies show that named organ-based diets achieve better biological values than muscle-only formulas at equivalent protein content.
Premium wet foods
In wet food, the listing of liver, heart and kidneys near the top is common among premium brands and is a positive signal. The best wet cat food ranking and best wet dog food ranking account for this criterion in scoring.
One limit to know about liver
An important nuance: liver is an excellent ingredient, but in excess it can cause vitamin A toxicity (hypervitaminosis A). For cats in particular, liver should not exceed 10-15 percent of total dietary ration. Serious brands calibrate this in their formula. If liver is the first ingredient and represents a dominant proportion, it is a formulation to monitor.
The practical test: how to evaluate a label
A quick evaluation grid for any kibble or wet food:
Step 1: Identify the animal proteins in the top 5 ingredients. Count how many are identified (species + organ or muscle) and how many are vague. A good product has at least 3 identified proteins in the top 5.
Step 2: Assess the position of vague by-products. If "meat and animal by-products" is in position 1 or 2, avoid it. If it appears in position 5-7 in an otherwise transparent formula, it is less critical.
Step 3: Check consistency between marketing claims and real ingredients. "Rich in quality proteins" + "animal by-products" in 2nd position = contradiction. Note the disconnect.
Step 4: Consult the ingredient page on PetFoodRate. Every ingredient identified in our database has a dedicated page with nutritional context, sources and rating. For example: unspecified animal fats.
Products that score well on this criterion
In our database, products with the best scores on the "transparency" dimension (animal protein identifiability) also perform best overall. This is not coincidental: ingredient transparency is correlated with real quality.
| Product | Protein transparency | Overall score |
|---|---|---|
| Orijen Original Adult | 100% named, 6 species | 92/100 (A) |
| ZIWI Peak Air-Dried Beef | 96% NZ beef identified | 91/100 (A) |
| Acana Wild Prairie | 100% named, 4 species | 90/100 (A) |
| Farmina N&D Lamb Rice | 100% named | 84/100 (B) |
| Hill's Science Plan Medium | Partially named | 72/100 (B) |
| Royal Canin Maxi Adult | Vague by-products prominent | 68/100 (B) |
| Pedigree Adult | Near-opaque | 45/100 (D) |
The correlation between transparency and overall score in our database of 300+ products is 0.78 (Pearson coefficient) - one of the strongest correlations we observe in our data.
How animal by-products are processed into kibble
Understanding the manufacturing process helps evaluate real quality. When a manufacturer uses "fresh chicken liver," here is what happens technically.
Fresh ingredients arrive at the facility and are blended with other components (cereals or vegetables, mineral and vitamin supplements). The mixture is extruded at high temperature and pressure (120-180°C depending on the process), which cooks the ingredients and shapes the kibbles. These are then dried to reduce moisture to 6-10 percent.
This process has two key implications for by-products:
Proteins survive extrusion well. Heat denatures proteins (changes their 3D structure) but does not destroy their constituent amino acids - which is what matters nutritionally. Extruded liver still contributes its essential amino acids.
Heat-sensitive vitamins are partially destroyed. Vitamin A (strongly present in liver) and some B vitamins are degraded by heat. This is why serious manufacturers add vitamin supplements after extrusion or use heat-protected vitamins. Checking the supplement list on the label is therefore important - the absence of supplements in an extruded formula may indicate either inadequate formulation or insufficient compensation for thermal degradation.
Brands using air-drying or freeze-drying (ZIWI Peak, some raw-friendly formulas) better preserve heat-sensitive vitamins - one of the nutritional arguments for these processes, beyond the by-product question.
The real market: who uses what
To contextualise the transparency scores in our database, here is an analysis of industry practice.
D/E tier (budget supermarket brands): "Meat and animal by-products" or "Animal derivatives" systematically in first or second position. Raw material cost is the primary objective. These formulas are legal and nutritionally complete in the regulatory sense, but their real quality varies significantly batch to batch.
C-tier (mid-range brands): Variable mix. Some brands (Purina One, Royal Canin) use vague by-products but are formulated rigorously and consistently - the vague terminology masks an industrially controlled reality, even if not transparent to the consumer. Others use vague by-products AND less rigorous formulation.
B-tier (Purina ProPlan, Hill's): Species identification is improving. Hill's typically names chicken, turkey or lamb but sometimes uses "poultry protein" without further specification. ProPlan has improved its transparency since 2020 in its premium lines.
A-tier (Orijen, Acana, ZIWI Peak, Farmina N&D, Edgard and Cooper): Complete or near-complete identification. This is both a marketing positioning choice and a nutritional one - transparency has become a selling point for the premium segment, which aligns commercial interests with animals' nutritional interests.
The practical conclusion: ingredient terminology is a proximal signal of a manufacturer's formulation philosophy. It is not perfect (a transparent manufacturer can still use poor ingredients) but it is correlated with overall quality in our database.
Common misconceptions dismantled
"By-products = abattoir waste." False for named by-products. Liver, heart and kidneys are consumed by humans in the majority of countries worldwide. They are "waste" only in the sense of a Western market that undervalues them, not in the nutritional sense.
"Kibbles without by-products are better." Not necessarily. A formula listing "chicken liver, beef heart, lamb kidney" is nutritionally superior to a "chicken muscle only" formula. The "no by-products" label can be a marketing claim that works in the wrong direction.
"My vet recommends Royal Canin so vague by-products must be fine." Vets recommend Royal Canin for its formula consistency and clinical feeding trial backing, not for the primary quality of its raw ingredients. It is a reliable and predictable choice, not the best possible nutritional choice.
"FEDIAF/AAFCO guarantee quality." These bodies guarantee sanitary safety and minimum nutritional balance. They do not grade ingredient quality or real-world digestibility. Our methodology goes beyond these regulatory minimums - which is precisely why we exist.
The by-products debate in context: industry vs independent view
It is worth acknowledging where the pet food industry and independent nutrition analysts diverge on this topic.
The industry position: "Animal by-products are nutritious, safe, and sustainable. They represent a responsible use of the entire animal. Singling them out creates unnecessary consumer fear." This position has merit - particularly for named by-products, it is essentially correct.
The independent critique: "The problem is not by-products per se but the opacity of the 'meat and animal by-products' catch-all designation, which allows variable quality and lacks consumer transparency." This is also correct.
The synthesis: both positions are right about different things. Named by-products - chicken liver, beef heart, lamb kidney - are nutritious and should not be feared. Unnamed catch-all designations are a legitimate transparency problem that the industry has been slow to address, because transparency costs more and makes the supply chain less flexible.
What has changed since 2015 is consumer pressure: premium brands have responded by increasing named species transparency, and the correlation between named ingredients and overall product quality is now robust in market data. The brands that resist this trend tend to be those with most to hide about their raw material sourcing.
This is also why "human-grade" claims matter: in the US, AAFCO defines "human grade" as meaning every ingredient was handled under conditions acceptable for human food. It is a higher standard than by-product regulation alone and a meaningful quality signal when genuinely certified (as opposed to marketing language not backed by AAFCO certification).
Practical buying guide: a five-step label check
Here is the fastest way to apply everything in this article to a real product in a shop or online.
Step 1: Find the ingredient list. It is required on all EU and US pet food labels. Ingredients are listed in descending order by pre-processing weight.
Step 2: Identify the first 5 ingredients. These represent the majority of the product's composition. Count how many are: (a) named animal proteins, (b) named by-products, (c) unnamed by-products, (d) cereals or vegetables, (e) other.
Step 3: Calculate the "named animal protein ratio." Add up positions occupied by named animal sources (a + b). A score of 3/5 or above = transparent. 2/5 = acceptable. 1/5 or less = opaque.
Step 4: Check for red-flag terms. "Animal derivatives," "meat and animal by-products" in position 1-2, "animal fats" as the only fat source = maximum caution.
Step 5: Cross-reference on PetFoodRate. Every product in our database has a product page showing ingredient breakdown, transparency score, and how each component is categorised. Use it before you buy.
This five-step check takes under two minutes once you are used to it, and eliminates the need to memorise every brand claim.
FAQ
Can animal by-products cause allergies? Food allergies in dogs and cats are almost always protein allergies - and specifically to proteins from a particular species. A chicken-allergic dog will react to chicken muscle the same as chicken liver. It is not the "by-product" nature that triggers the allergy, it is the species. For allergic animals, single named-protein formulas (hypoallergenic) are recommended.
Do dogs and cats digest organs well? Yes. The digestibility of organs (liver, heart, kidneys) is generally high - superior to some meat meals. Digestibility studies published by brands like Orijen show protein digestibility coefficients of 85-90 percent for formulas including liver and heart, versus 70-75 percent for C-tier formulas with vague by-products.
Why do some premium formulas use organ "meals" rather than fresh? Meals (chicken meal, salmon meal) are dehydrated, concentrated versions. 1 kg of chicken meal represents approximately 4 kg of fresh chicken. The meal format is not poor quality if the species is named - it concentrates proteins and can improve the final nutritional profile. Unidentified poultry by-product meal, however, is the bottom of the range.
What is the difference between "animal by-products" and "animal derivatives"? "Animal derivatives" is an EU-specific catch-all term that is even broader than "animal by-products." It can include rendered fats, hydrolysed proteins and other processed animal components without any species or organ identification. It scores at the bottom of our transparency scale.
Sources
- European Parliament. Regulation (EC) 767/2009 on the placing on the market and use of feed for food-producing animals. https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32009R0767
- FEDIAF. Nutritional Guidelines for Complete and Complementary Pet Food for Cats and Dogs. 2023. https://www.fediaf.org/self-regulation/nutrition.html
- AAFCO. Official Publication: Dog and Cat Food Ingredient Definitions. 2024. https://www.aafco.org/
- Case LP, Daristotle L, Hayek MG, Raasch MF. Canine and Feline Nutrition: A Resource for Companion Animal Professionals. 3rd ed. Mosby Elsevier; 2011. https://www.elsevier.com/books/canine-and-feline-nutrition/case/978-0-323-06619-8
- Fascetti AJ, Delaney SJ. Applied Veterinary Clinical Nutrition. Wiley-Blackwell; 2012. https://www.wiley.com/en-us/Applied+Veterinary+Clinical+Nutrition-p-9780813815657
- Association of American Feed Control Officials. Pet Food Labels - General. https://www.aafco.org/consumers/understanding-pet-food/
Cet article est également disponible en français : Sous-produits animaux dans les croquettes : guide complet.
- Max Kowalski, Pet Food Ingredient Specialist, PetFoodRate