By-product is a legal term for the parts of a slaughtered animal that are not prime cuts, and most of those parts are organ meat, bone and blood — roughly the tissues a cat would eat first from a mouse. A chicken by-product meal often runs 60 to 65 percent protein on a dry matter basis, at or above the 55 to 62 percent in chicken meals sold as premium. The label word tells you which tissues went in. It does not tell you whether the food is good.
The decision is arithmetic, not vocabulary. Three edible classes cover nearly every by-product on a label, two label traps distort the comparison, and four checks settle most arguments in under 5 minutes.
What the word by-product actually covers
AAFCO defines poultry by-products as the non-rendered, clean parts of a carcass other than flesh: heads, feet, viscera and similar tissue. Meat by-products extend the idea to mammals and exclude hair, horns and hooves. These are tissue definitions, not freshness or safety grades. Rendering at 115 to 145 C is what turns wet tissue into a stable meal at 4 to 8 percent moisture.
Three tissues dominate in practice: organ meat, bone and connective tissue, and blood or glandular tissue. A formula listing 2 or 3 of them is not automatically worse than one listing a single muscle cut.
The 3 edible classes and what they bring
Class 1 is named organ meat. Liver supplies vitamin A, copper and iron; heart is working muscle with taurine at 0.15 to 0.25 percent of its dry matter. Liver at 5 to 10 percent of the formula covers vitamin A without a synthetic top-up, while very high inclusion pushes vitamin A past 100,000 IU per kg DM.
Class 2 is bone and cartilage, usually arriving as a meal with ash at 14 to 22 percent of its own dry matter. This class decides calcium and phosphorus in the finished food: about 1.0 to 1.6 percent calcium and 0.8 to 1.3 percent phosphorus on a dry matter basis, at a ratio near 1.1 to 1.3 to 1. Bone is also where ash comes from, and ash is the number most labels hide.
Class 3 is blood, lung, spleen and glandular tissue. Blood meal is 80 to 90 percent protein on a dry matter basis and carries iron at 1,500 to 2,500 mg per kg, so it appears at 2 to 5 percent for palatability, not as a protein source.
Nutrient equivalence, converted to dry matter
Nothing is comparable until you remove water. Dry matter equals 100 minus moisture, so tissue at 70 percent moisture has 30 percent dry matter and every other number roughly triples per unit of dry matter. Values are typical published ranges, not one brand.
| Tissue (as fed) | Moisture % | Protein % | Fat % | Ash % | Protein % DM | Fat % DM |
|---|---|---|---|---|---|---|
| Chicken by-product meal | 6 | 60 | 12 | 14 | 63.8 | 12.8 |
| Chicken meal | 6 | 62 | 13 | 12 | 66.0 | 13.8 |
| Fresh chicken | 70 | 18 | 8 | 1 | 60.0 | 26.7 |
| Pork liver | 72 | 15 | 4 | 1.3 | 53.6 | 14.3 |
| Poultry bone meal | 5 | 50 | 9 | 20 | 52.6 | 9.5 |
Two rows carry the argument. By-product meal lands within 3 points of chicken meal on protein. Fresh chicken looks like a premium first ingredient at 60 percent protein dry matter, but only after you delete the water it was weighed with. Fat moves the other way: fresh tissue concentrates to 26.7 percent of dry matter, fine in a 4,000 kcal per kg food and heavy in a 4,400 kcal per kg food for an indoor cat. That trade-off is the same one behind wet versus dry math.
Trap 1: ingredient splitting hides the real total
Ingredients are listed by weight as fed, and fractions of one tissue need not be combined. Split 30 percent chicken into entries of 12, 10 and 8 percent and each drops below the 15 percent first-slot threshold, so a named meal takes first place and the label reads cleaner than the formula is.
Water makes it worse. In a 10 kg batch, 3 kg of fresh chicken at 70 percent moisture contributes 0.9 kg of dry matter; 2 kg of meal at 6 percent moisture contributes 1.88 kg. The fresh meat is 50 percent heavier on the label and delivers 52 percent less dry matter. When fresh meat sits in slots 1 and 2 followed by 3 meals, assume the meals carry the protein.
Trap 2: no-by-product claims and the price premium
No by-products is a marketing position, not a nutritional one. Formulas making the claim run 8 to 14 dollars per kg against 5 to 8 dollars per kg for by-product-based foods at similar protein: a 40 to 70 percent premium that buys a different tissue mix, not a measured difference in digestibility. That premium is wasted if the cat refuses the food for 7 days.
A second version of the same trap is unnamed species. Meat by-products could be any mammal; chicken by-product meal is one species and one tissue list. For an elimination trial the named meal is the safer ingredient. For the everyday bag both are legal and both can be complete.
The 4 checks that decide a bag
- Find the completeness statement. It must name the life stage; anything labeled for intermittent feeding is a topper at any protein level.
- Convert protein to dry matter. Adult maintenance needs 26 percent DM as a floor, growth 30 percent, and decent dry foods sit at 32 to 40 percent.
- Check ash and phosphorus. Above 8 percent ash DM or 1.2 percent phosphorus DM is a poor fit for a cat over 10 years old.
- Confirm taurine at 0.10 percent DM for dry food, 0.20 percent for canned, and a named animal in the first ingredient.
When by-products are the wrong choice
Three situations argue against a high-ash formula. A cat with CKD on a renal diet needs phosphorus at 0.3 to 0.5 percent DM, and bone-heavy meals fight that target. A cat in an 8 to 12 week elimination trial needs one named protein, so a multi-tissue meal with 4 species is unusable. A kitten under 6 months on a 4,300 kcal per kg food needs a tighter calcium-to-phosphorus ratio than a 20 percent ash meal allows.
For everything else the tissue question is secondary. A 4 kg indoor cat eating 45 to 55 g of a 3,800 kcal per kg food gets its energy either way, about 9 g of protein per 100 kcal; what changes is ash load, phosphorus, and 5 to 9 dollars a month. If you are weighing a switch, run the numbers on how much wet food a cat needs before adding a second format.
A 4-step routine for the store aisle
- Photograph the guaranteed analysis on 3 candidate bags before comparing price; dry matter math does not work from memory.
- Compute protein DM and phosphorus DM on your phone and strike anything under 30 percent protein or over 1.2 percent phosphorus.
- Read the first 5 ingredients for split fractions and unnamed species; for plant hazards use the toxicity checker, not the bag.
- Buy 1 to 2 kg first and transition over 7 days at 25, 50, 75 and 100 percent before committing to a 5 kg bag.
Terms mentioned in this article
Frequently asked
Are by-products in cat food worse than muscle meat?
Not as a category. Organ meat and bone carry nutrients muscle meat lacks, and a rendered by-product meal often tests 60 to 65 percent protein on a dry matter basis against 55 to 62 percent for premium chicken meal. The finished guaranteed analysis decides quality, not the tissue word.
Why do some labels list chicken three times?
Ingredients are sorted by weight as fed, and fractions of one tissue may appear separately. Splitting 30 percent chicken into 12, 10 and 8 percent entries pushes each below the first-slot threshold, so a named meal takes first place. Add the fractions before judging the order.
Should I avoid ash in cat food?
You cannot avoid it, because ash is the mineral residue left after combustion and every meat contains minerals. Keep dry food under 8 percent ash on a dry matter basis and under 1.2 percent phosphorus, especially for cats over 10 years old with rising kidney values.
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