Meat By-Products in Cat Food: Good or Bad for Cats?

Meat by-products in cat food are not inherently bad, and in many cases they supply nutrients that cats genuinely need. Organs like liver, kidney, and heart are closer to what a cat would eat in the wild than a boneless chicken breast is. The real question is not whether by-products belong in cat food but how they were sourced, processed, and preserved before reaching the can or kibble bag. That distinction between the raw ingredient and the finished product is where the science gets interesting and where the marketing claims on both sides tend to fall apart.

What “Meat By-Products” Actually Means

The term “by-product” sounds like waste, which is exactly why premium pet food brands use it as a selling point when they leave it off the label. But in regulatory terms, meat by-products are the parts of a slaughtered animal other than the skeletal muscle meat that humans typically eat. That includes liver, kidneys, lungs, spleen, intestines, blood, and sometimes bone. It does not include hair, hooves, horns, or teeth, all of which are explicitly excluded by feed-ingredient definitions.

For a cat, many of these organs are nutritional powerhouses. Liver is dense in vitamin A, iron, and B vitamins. Heart is rich in taurine, an amino acid cats cannot synthesize on their own and will go blind or develop heart failure without. Kidneys provide additional B vitamins and trace minerals. A wild cat eating a mouse consumes virtually the entire animal, organs and all. Research on whole-prey digestibility in cats found that the average dry-matter digestibility of whole rats was about 90%, with amino acid digestibility across the whole prey exceeding 85%.¹ Among individual organs, muscle was the most digestible at nearly 100%, but organs like liver and kidney also showed amino acid digestibility above 90%. The only significant holdout was bone, which dropped to around 59% digestibility.

So the raw biological materials that go into by-product meals are, in their natural state, highly digestible and nutritionally appropriate for cats. The complication is that what arrives in a can of cat food has gone through an industrial process that can change the picture substantially.

How Rendering and Heat Processing Change the Nutritional Picture

Most by-products in dry cat food go through rendering, a process that cooks animal tissues at high temperatures to kill pathogens, drive off moisture, and separate fat from protein. The resulting dry, shelf-stable powder, labeled as “poultry by-product meal” or “meat and bone meal,” is a concentrated protein source. But the heat involved is a double-edged sword.

Research on poultry by-product rendering found that as processing temperature and time increased, levels of key amino acids like lysine, methionine, and cystine dropped significantly.² There was an interesting wrinkle: in the first 40 to 60 minutes of heating, lysine and cystine levels actually rose slightly from their starting values, likely because moisture loss concentrated the remaining protein. After that initial window, continued heating drove those amino acids steadily downward. The bottom line is that a gently rendered by-product meal and an aggressively cooked one can look similar on a guaranteed analysis panel yet differ meaningfully in how much usable protein your cat actually absorbs.

This is a well-recognized problem in the industry. Excessive heat damages proteins and decreases their quality and digestibility, and ongoing research is aimed at giving renderers better guidance on cooking procedures that balance food safety with nutritional preservation.³ Wet cat food, which undergoes retort sterilization but generally at lower temperatures than dry rendering, tends to preserve amino acid profiles somewhat better, though it introduces its own quality concerns.

The Batch Variability Problem

One of the most underappreciated issues with by-product meals is that two bags of the same brand can contain meaningfully different ingredients depending on what went into the rendering plant that week. A study characterizing commercial poultry by-product meal found that while crude protein content was relatively consistent, with coefficients of variation around 5 to 7%, other nutritional markers swung widely. Fat content varied by 15 to 21%, collagen by 21 to 30%, and mineral matter by roughly 20%.⁴ Processing time was especially inconsistent, with variation exceeding 27% even within the same facility. The researchers concluded that limiting the amount of bone in the raw material and better controlling processing time would help standardize the finished product.

A separate analysis comparing feed-grade and pet-food-grade poultry by-product meal found that nutrient variability was more pronounced in the feed-grade product.⁵ Pet-food-grade meals, which typically face tighter specifications from manufacturers, showed somewhat narrower ranges. This matters because when your cat’s food lists “poultry by-product meal” as a primary ingredient, the nutritional reality of that ingredient depends not just on what species of animal it came from, but on which parts went in, how much bone was included, and how long and hot the batch was cooked.

The oxidative stability of by-product meal is similarly variable. A study tracking poultry by-products from raw material through finished meal found that digestibility and oxidation resistance were both highly inconsistent across commercial samples, driven primarily by differences in drying intensity and antioxidant content.⁶ High processing temperatures, especially when paired with longer cook times, had a clear negative impact on digestibility.

Phosphorus, Bone Content, and Kidney Health

This is where by-products get genuinely complicated for cats, especially older ones. Cats are prone to chronic kidney disease, and dietary phosphorus is a significant factor in how quickly that disease progresses. By-product meals that include a lot of bone are naturally high in phosphorus and calcium, delivered mainly as inorganic mineral salts. Research on meat and bone meal has confirmed that these products tend to carry high ash content, which is essentially the mineral residue left after combustion and a rough proxy for bone inclusion.⁷

Why does that matter? The form phosphorus takes in a cat’s diet affects how the kidneys handle it. Research on feline phosphorus metabolism has found that highly water-soluble inorganic phosphorus sources, like sodium phosphates, force the kidneys to excrete far more phosphorus than less soluble forms. In one study, cats fed a diet with sodium monophosphate excreted more than three times the renal phosphorus of cats fed calcium monophosphate, and over half the cats in the sodium phosphate group developed glucosuria, a sign of kidney stress that was absent in the other group.⁸

A review of phosphorus homeostasis in cats concluded that when phosphate concentrations in the kidney tubules exceed a certain threshold for a significant part of the day, structural kidney damage follows.⁹ The same review noted that carefully formulated diets containing up to 1 gram per megacalorie of inorganic phosphorus could be fed without detectable adverse effects on kidney health, as long as the resulting tubular phosphate concentrations stayed below a safe threshold. The practical takeaway is that by-product meals with heavy bone inclusion can push phosphorus levels above what a cat’s kidneys comfortably handle, particularly if the phosphorus is in a highly soluble inorganic form. This is less of a concern with organ-heavy by-products that contain relatively little bone.

Freshness, Oxidation, and Hidden Safety Issues

By-products are perishable tissues, and the time between slaughter and processing matters. A study analyzing commercial wet cat foods found measurable signs of oxidative damage in some samples, with markers of both fat oxidation and protein oxidation present at levels that indicated degradation.¹⁰ The same study detected histamine, putrescine, and cadaverine, biogenic amines that form when bacteria break down amino acids. Their presence is a signal that the raw materials sat around longer than ideal before being processed, or that the raw materials were of suboptimal quality to begin with.

None of these amines were at acutely toxic levels in the tested products, but their presence tells you something about the gap between the best and worst examples of by-product use. A manufacturer sourcing fresh organ meats from a nearby slaughterhouse and processing them within hours is producing a fundamentally different product than one receiving rendered meal from mixed, older raw materials. Both products can legally be labeled as containing “meat by-products,” which is part of why the ingredient list alone is such a poor guide to actual quality.

Why By-Products Are Everywhere in Cat Food

Economics plays an enormous role. The rendering industry in the United States processes roughly 25 million tons of animal by-products each year, and rendered products are valued across livestock, aquaculture, and pet food industries for their high protein content, digestible amino acid levels, mineral availability, and relatively low cost.¹¹ From an environmental standpoint, using these materials in pet food rather than sending them to landfill is a meaningful waste-reduction strategy.

The cost difference is not trivial. A study developing pet food with 50% poultry by-products powder found the production cost was roughly 205 rupees per kilogram, compared to about 366 rupees per kilogram for a similar product made with chicken meat powder, a reduction of more than 40%.¹² That cost saving flows through to shelf price, which is one reason by-product-based foods dominate the budget and mid-range segments. Brands marketing “no by-products” are essentially saying they use only the cuts that compete with human food demand, which costs more and is not necessarily more nutritious for a cat.

Do Cats Actually Prefer By-Products?

Cats are notoriously picky eaters, and the pet food industry invests heavily in palatability research. Interestingly, by-product-derived ingredients are often the key to making a food appealing. A study investigating chicken liver protein hydrolysates as cat food attractants found that specific hydrolysate formulations significantly influenced both how much cats ate and which food they chose first.¹³ The researchers analyzed the aroma compounds generated during hydrolysis and found that the specific volatile profile drove preference. Liver-based flavor coatings are standard in the industry, including on many “no by-products” kibbles, which is an irony worth noting.

There is also some evidence that enzymatic processing of by-products can create bioactive compounds beyond simple nutrition. Research on enzymatically hydrolyzed poultry by-product meal found that the hydrolyzed version showed much higher inhibitory activity against angiotensin-converting enzyme (ACE), a key player in blood pressure regulation, compared to conventionally processed meal. Cats fed the hydrolyzed diet tended to show lower serum ACE activity, though the difference did not quite reach statistical significance.¹³ This is early-stage research, but it hints at a future where processing methods are tuned not just for palatability and digestibility but for specific health-promoting effects.

Reading the Label More Usefully

Given everything above, here is what actually matters when you are evaluating a cat food that contains by-products:

Named species: “Chicken by-products” or “turkey by-product meal” tells you the animal source. Generic “meat by-products” or “animal by-product meal” with no species named is a flag that the sourcing may be less controlled.
Ash content: High ash, usually above 8 to 10% on a dry-matter basis, suggests heavy bone inclusion. For cats with kidney concerns, lower ash is generally preferable.
Phosphorus levels: Look for the guaranteed analysis or contact the manufacturer. Cats with kidney disease do best on phosphorus-restricted diets, and bone-heavy by-product meals push this number up.
Meal vs. fresh: “Chicken by-products” in wet food means relatively minimally processed organ tissues. “Chicken by-product meal” means rendered, dried, and ground, with greater potential for heat damage to amino acids but also more concentrated protein per gram.

The presence or absence of by-products on a label is a poor shorthand for quality. A well-sourced, gently processed by-product meal from a reputable manufacturer can deliver excellent nutrition. A poorly rendered, bone-heavy, oxidized by-product meal from inconsistent raw materials is a different product entirely, even if the label reads the same.

The Sustainability Angle

One dimension that rarely comes up in the “good or bad” debate is ecological. Cats in the United States alone consume billions of dollars’ worth of animal protein annually. If every cat food replaced by-products with human-grade muscle meat, the demand on livestock production would increase substantially, with corresponding increases in land use, water use, and greenhouse gas emissions. By-products represent tissues that would otherwise become waste. The rendering industry frames this as a recycling process, and the framing is not wrong: converting slaughterhouse remnants into pet nutrition captures value from animals already being raised for human consumption rather than requiring additional animals.¹¹

Whether that consideration factors into your purchasing decision is personal. But the popular framing of by-products as “garbage” and muscle meat as “real food” maps poorly onto both the nutritional science and the environmental reality. For a species that evolved eating whole prey, organ meats are not second-class protein. The challenges with by-products are real, but they are challenges of processing and quality control, not of the raw materials themselves.

1
Oxford Academic / Journal of Animal Science. Protein quality of a small mammal prey and its body organs for felids
2
LWT – Food Science and Technology. Relationship of rendering process temperature and time to selected quality parameters of poultry by-product meal
3
PubMed Central. Rendering Effects on pet Food Ingredients
4
PubMed Central. Characterization of the variations in the industrial processing and nutritional variables of poultry by-product meal
5
Journal of Applied Poultry Research. Nutrient Compostion of Feed-Grade and Pet-Food-Grade Poultry By-Product Meal
6
Animal Feed Science and Technology. Oxidative stability and nutritional quality of poultry by-product meal: An approach from the raw material to the finished product
7
PubMed. Digestibility for dogs and cats of meat and bone meal processed at two different temperature and pressure levels
8
PubMed. Renal phosphorus excretion in adult healthy cats after the intake of high phosphorus diets with either calcium monophosphate or sodium monophosphate
9
PubMed. New concepts in phosphorus homeostasis and its impact on renal health with particular reference to the cat
10
PubMed Central. Physicochemical Quality and Chemical Safety of Commercial Wet Cat Food: Composition, Oxidation, Biogenic Amines, and Trace Elements – Section: 3.2 pH, Oxidative Stability and Toxic Trace Minerals in Commercial Wet Cat Food
11
Journal of Animal Science. COMPANION ANIMALS SYMPOSIUM: Rendered ingredients significantly influence sustainability, quality, and safety of pet food
12
Animal Nutrition and Feed Technology. Utilization of poultry slaughter byproducts to develop cost effective dried pet food
13
PubMed. Generation of Olfactory Compounds in Cat Food Attractants: Chicken Liver-Derived Protein Hydrolysates and Their Contribution to Enhancing Palatability