The truth about by-products in pet food: a fear of a word, not a risk
The truth: An animal by-product, in pet food, is a part of the carcass other than skeletal muscle: liver, kidney, heart, lung, spleen and similar tissues that are rarely sold over a butcher's counter in some food cultures. The word triggers unease in many owners, who picture waste or low-grade scraps. The regulatory and nutritional reality is close to the opposite. In the European Union, only Category 3 material, defined as coming from animals passed fit for human consumption at slaughter inspection, may enter pet food (Regulation (EC) 1069/2009). And offal ranks among the most nutrient-dense components of any ration. The most useful thing an owner can know is that the distrust of by-products stems from the cultural connotation of the word, not from a demonstrated risk (FEDIAF, 2024). This article separates the fear of a term from the evidence behind it.
Last updated :General documentary information. For an individual animal, a veterinarian's advice takes precedence over any online content.
What a by-product actually is
The term describes an origin, not a quality grade. By-products group the edible tissues other than muscle flesh taken from slaughtered animals: liver, kidney, lung, spleen, heart, and sometimes blood or rind. The regulatory definitions are tight in both major frameworks. In Europe, Regulation (EC) 1069/2009 sorts all animal material into three risk categories and admits only Category 3, the lowest risk, into animal feed. In the United States, AAFCO publishes named definitions such as "poultry by-product" that explicitly exclude hair, horns, teeth, hooves, feathers, beaks and feet beyond set thresholds (AAFCO). Both frameworks bound the material tightly; neither permits a bin of indiscriminate waste.
A surprising point follows from this. Many of the cuts classed as by-products in the pet food chain are prized human foods in other cuisines. The boundary between a by-product and a delicacy is therefore commercial and cultural rather than biological. The by-product is not a residue but a worthy material poorly named.
Why offal is nutritionally valuable
Far from being inferior to muscle meat, organ tissue is among the densest sources of micronutrients in a carnivore's natural diet. Liver concentrates vitamin A, haem iron, copper, zinc and B-group vitamins at levels well above lean muscle (FEDIAF, 2024). The WSAVA notes that organs belong to the natural diet of carnivores, and that in a prey carcass they supply a share of micronutrients far larger than their relative weight. A wild cat or dog eating prey does not discard the liver and heart; those tissues are part of why the prey is nutritionally complete.
The level of evidence on the value of Category 3 offal is high, resting on long-standing, reproducible composition data (FEDIAF, 2024). This is one of the better-established facts in pet nutrition, which is what makes the persistent fear of the word so striking.
The categories, and what is excluded
The European system makes the safety floor explicit, and seeing the three tiers laid out clarifies why a compliant by-product is not waste.
| Category | Example material | Permitted in pet food? |
|---|---|---|
| Category 1 | High-risk material, certain banned tissues | No, excluded |
| Category 2 | Other unfit material | No, excluded |
| Category 3 | Liver, heart, lung of animals fit for human consumption at inspection | Yes, the only permitted tier (Regulation (EC) 1069/2009) |
Unfit waste falls under Categories 1 and 2 and is banned from animal feed, while the Category 3 by-product comes from inspected, healthy animals (Regulation (EC) 1069/2009). A product made under EU rules therefore cannot legally contain Category 1 or 2 material. Regulation (EC) 767/2009 then governs how the feed is labelled and named. The framework guarantees a controlled origin.
Alt text: "Diagram of the three EU animal by-product risk categories, with only Category 3 permitted in pet food."
The real issue: transparency, not toxicity
If by-products are safe and nutritious, why do they have such a poor reputation among careful owners? The genuine caveat is not toxicity but the variability of a generic blend. The law permits group designations such as "meat and animal by-products" without naming the species, which means a manufacturer can stay fully compliant while remaining vague (Regulation (EC) 767/2009). A generic meal or by-product with no species named may mix heterogeneous origins from batch to batch, which complicates traceability (FEDIAF, 2024). Two equally legal labels can therefore inform very unequally.
This is a traceability argument, not a safety one. With equal information, a named entry such as chicken liver tells you more than a vague meat and animal by-products. The thing to scrutinise is the precision of the label, not the presence of the term. A named by-product from a single species is a transparent, high-value ingredient. An unnamed generic blend is legal and safe but tells you less. Quality is therefore judged on the precision of the label, not on rejecting a category.
How to read a by-product line
Three practical cues separate a transparent label from an opaque one:
- Look for a named species and tissue. "Chicken liver" or "salmon" is more informative than "meat and animal by-products" or "meat derivatives".
- Treat the absence of a species name as a transparency limit, not a danger sign. The material is still bound by Category 3 rules; you simply know less about its consistency batch to batch.
- Remember that a named meal, such as chicken meal, is governed by AAFCO and FEDIAF naming rules and is a concentrated, legitimate protein source, not a euphemism for waste.
The same logic applies to animal meals, which are simply rendered, dehydrated tissues. A named meal is a quality ingredient; a generic one is merely less transparent. Neither is inherently low grade.
By-products in the carnivore's natural diet
A useful way to test the fear is to ask what a dog or cat actually ate before it ate from a bag. A wild or feral carnivore consuming prey does not stop at the muscle; it eats the organs, often first, because they are the densest source of the vitamins and minerals it needs. The liver, kidney, heart and other tissues that the pet food industry labels by-products are, in the prey carcass, simply the most nutritious part of the meal. A diet of pure muscle meat would in fact be unbalanced for a carnivore, short on several micronutrients that organs supply in abundance.
Seen this way, the inclusion of named organ tissue in a complete food is not a corner cut but a step towards the composition the animal evolved to eat. The WSAVA's observation that organs belong to the natural diet of carnivores is not a rhetorical flourish; it reflects the basic biology of how these species met their nutrient needs. The cultural reflex that ranks muscle meat above offal is a human food preference, and it does not map onto what is nutritionally best for a dog or a cat.
Named meals are not a euphemism either
The same suspicion that attaches to by-products often spreads to animal meals, such as chicken meal or lamb meal, which some owners read as a sign of low quality. The reality is that a meal is simply a rendered, dehydrated tissue: the water has been removed, leaving a concentrated protein source that is stable and, weight for weight, richer in protein than fresh meat. A named meal is governed by AAFCO and FEDIAF naming rules, and it is a legitimate, often desirable ingredient (AAFCO; FEDIAF, 2024).
The distinction that matters is, once again, naming rather than category. A named meal from a single species tells you what you are getting; a generic meal with no species named is legal and safe but less transparent, because it may draw on heterogeneous origins from batch to batch. Two products listing the same word can differ depending on the freshness of the incoming material and the rendering process, which is precisely why the precision of the label, not the presence of the word meal, is what carries the quality signal. An owner who rejects a food the moment they see meal or by-product is discarding the very arithmetic that would have told them whether the food was good.
Why the fear persists
It is worth naming why a well-evidenced ingredient carries such a stubborn stigma. The word by-product implies a leftover, and marketing for some premium foods has leaned on that implication, advertising "no by-products" as if it were a quality guarantee. As with the term filler, this borrows authority from a fear the rules never validated. A food can be excellent while containing named organ meats, and a food can be mediocre while advertising their absence. The honest position is that the category is safe and nutritious by the weight of evidence, the only real variable is how transparently it is declared, and an owner is better served by reading the label precisely than by avoiding a word.
A balanced reading of the term
The fairest summary is that by-product is a neutral word that has been loaded with a value judgement it does not deserve. The level of evidence on the nutritional value of Category 3 offal is high and long-standing, while the evidence of any toxicity at the regulated level is absent (FEDIAF, 2024; Regulation (EC) 1069/2009). What remains genuinely variable is transparency, and that variability is a feature of how a particular label is written, not of the category as a whole. An owner who internalises this stops asking "does it contain by-products" and starts asking "how precisely is each ingredient named", which is the question that actually separates one food from another.
This also guards against the opposite error, treating "no by-products" as a guarantee of quality. A food can advertise the absence of by-products while being built on a single generic muscle-meat source of unstated origin, which is less informative than a food that names chicken liver and chicken heart. The presence or absence of the word tells you almost nothing on its own. The traceability of the naming tells you a great deal, and it is available to anyone willing to read the full ingredient list rather than reacting to a single term.
Where to read more (truth about)
The questions on whether by-products are dangerous, what they actually are, and why some labels stay vague are handled in our controversial ingredients FAQ and our reading and decoding a label FAQ. For structured help, the are by-products bad guide and the spotting fear marketing guide show how to read these claims. The category itself is defined in our entry on meat and animal by-products.
The takeaway (truth about)
By-products are bound by strict EU and US rules, only the lowest-risk Category 3 material may enter pet food, and organ tissue is among the most nutrient-dense parts of any carcass. The distrust of the word reflects culture, not evidence. The one thing worth scrutinising is transparency: a named species and tissue tells you far more than a generic blend, and that, not the term itself, is where the quality difference actually lives.