What Is an Animal Byproduct? Uses and Examples

An animal byproduct is any material derived from an animal that is not the primary cut of meat sold for human consumption. This includes organs, bones, blood, fat trimmings, hides, hooves, feathers, wool, and intestines. These materials account for a substantial share of a slaughtered animal’s total weight, and rather than going to waste, they feed into dozens of industries you encounter daily without realizing it. The gelatin in your gummy vitamins, the heparin in a hospital IV drip, and the tallow-derived ingredients in your bar of soap all trace back to what the meat industry considers secondary material.

What Counts as a Byproduct

When a cow, pig, or chicken is processed for its steaks, chops, or breast fillets, roughly half the animal’s body weight ends up as something other than retail meat. The exact proportion varies by species and the market in question, but the leftover mass is enormous. Globally, inefficient use of these materials represents both lost revenue and a significant waste-disposal burden.¹ The category is broad and includes:

• Soft tissues: organs (liver, heart, kidneys, lungs), blood, intestines, and fat trimmings
• Hard tissues: bones, hooves, horns, and antlers
• Skin and coverings: hides, pelts, feathers, and wool
• Glandular material: pancreas, thyroid, and pituitary glands

Some of these materials, like liver or tripe, are edible and valued in many cuisines around the world. Others, like hooves or blood, are routed to industrial processing. The distinction between “edible byproduct” and “inedible byproduct” matters because it determines the regulatory pathway and the kind of processing the material undergoes.

How Byproducts Are Processed

The workhorse of the animal byproduct industry is rendering, a thermal process that has been in use for well over a century. At its core, rendering involves two steps: cooking the raw material to drive off moisture, then separating the melted fats from the remaining protein solids.² The fat fraction becomes tallow or lard depending on the source animal, while the protein solids are dried and ground into meals like meat-and-bone meal or poultry byproduct meal.

This cooking step also serves a critical food-safety function. Studies on poultry rendering have shown that the heat applied during processing is sufficient to achieve a seven-log reduction of Salmonella, meaning it kills more than 99.99999 percent of the bacteria present in raw offal.³ However, pathogen destruction is not always a clean, linear process. Research on beef rendering materials has found that certain Salmonella strains can appear to be eliminated at one time point and then reappear at a later one during extended heat treatment, a reminder that proper protocols and sanitary conditions matter.⁴

Compared to composting or landfill disposal, rendering recovers far more economic value from the same raw material. One review found that the economic value of rendered products is at least three times greater than what anaerobic digestion yields and at least five times greater than the value added to compost by including the same quantity of meat byproducts.⁵ So rendering is not just about hygiene; it is an economic engine that turns low-value scraps into marketable commodities.

Pet Food and Animal Feed

If you have ever read the ingredient panel on a bag of dog food and seen “poultry byproduct meal” or “chicken meal,” you were looking at rendered animal byproducts. These meals are concentrated protein sources, and they are one of the largest end markets for the rendering industry. There is a quality spectrum, though. Pet-food-grade poultry byproduct meal tends to have higher protein content, less ash, lower calcium, and better amino acid digestibility than feed-grade versions of the same ingredient.⁶

The degree of processing matters, too. Research comparing different chicken-based ingredients found that chicken meal, which undergoes more intensive thermal processing, had lower nutrient digestibility than less processed alternatives. True digestibility for most amino acids in chicken meal fell between 75 and 85 percent, and its amino acid profile scored below 100 percent on a quality index, suggesting it may not supply all essential amino acids when used as the sole protein source at minimal inclusion levels.⁷ In practice, commercial pet foods blend multiple protein sources, so this limitation rarely shows up as a deficiency in a finished product. But it does explain why some premium pet food brands advertise “whole chicken” or “deboned chicken” rather than “chicken meal” as a selling point.

Gelatin and Collagen

Gelatin is one of the most familiar animal byproducts, found in everything from marshmallows and gummy candies to pharmaceutical capsules and photographic film. It is produced by partially breaking down collagen, the structural protein found abundantly in animal skin, bones, and connective tissue.⁸ The raw materials are cheap and plentiful: cattle hides left over after leather tanning, pig skins, and bones that have already had their marrow extracted.

The extraction process involves a chemical pretreatment step before the collagen is heated in water to dissolve it. The choice of pretreatment, whether acid, alkaline, or enzyme-based, affects the final product’s strength, clarity, and gelling ability. Research on cattle-derived gelatin has found that alkaline pretreatment produces the highest quality, with strong gelling and favorable physical properties.⁹ This matters commercially because gelatin’s usefulness depends on its gel strength, which the industry measures on a standardized “Bloom” scale.

Collagen peptides, a related product, have become a booming supplement category marketed for skin, joint, and gut health. These are produced from the same animal tissues but are broken down further than gelatin, making them soluble in cold water. The raw material is the same; the processing just goes one step further.

Pharmaceutical and Medical Uses

Some of the most life-saving applications of animal byproducts happen in medicine. Heparin, the blood-thinning drug used in surgeries, dialysis, and treatment of blood clots, is extracted from the intestinal lining of pigs or, less commonly, from bovine heart tissue. The mucosa is treated with enzymes and chemicals to isolate the active compound, which is then purified into a pharmaceutical-grade salt.¹⁰ The global supply of heparin depends almost entirely on pork processing, which creates a supply-chain vulnerability that public health experts have flagged, particularly given periodic disruptions from swine disease outbreaks.

Enzymes are another major category. Trypsin, a digestive enzyme used in food processing, pharmaceutical manufacturing, and textile production, can be purified from the waste pancreas of slaughtered animals. Research on trypsin extracted from sheep pancreas has demonstrated that the resulting enzyme has high specific activity and hydrolysis efficiency, along with useful heat and alkaline resistance that make it well suited to industrial applications.¹¹ Other glandular byproducts have historically yielded insulin (from pig and cow pancreases, before recombinant DNA technology largely replaced this), thyroid hormones, and adrenal extracts.

Tallow in Soap, Chemicals, and Industry

Tallow, the rendered fat from cattle, is one of the oldest and most versatile industrial materials derived from animal byproducts. It has been the foundation of soapmaking for centuries, and it remains a major raw material in the oleochemical industry, where it is split into fatty acids and glycerol. These derivatives feed into the production of detergents, surfactants, cosmetics, candles, lubricants, and rubber compounds.¹² Stearic acid, one of the fatty acids derived from tallow, shows up in products as varied as tire rubber, crayons, and plastic stabilizers.

The scale of this industry is significant. Inedible tallow, meaning fat not suitable for human food, is a major feedstock for fatty acid manufacturing.¹² If you pick up a bar of commercial soap and see “sodium tallowate” on the label, that is saponified beef fat. Many people use tallow-derived products every day without any awareness of the connection to the meat industry.

Lanolin and Personal Care Products

Wool grease, the waxy substance that coats sheep’s fleece and protects it from weather, is another animal byproduct with a long commercial history. After shearing, raw wool is scoured with water and detergent to remove the grease, which is then refined into lanolin. The refining process involves several stages: acid treatment to remove impurities, alkaline treatment to neutralize free fatty acids, adsorption with activated carbon, vacuum heating to strip residual odors and pesticide traces, and finally bleaching with hydrogen peroxide to lighten the color.¹³

The end product is a pale, nearly odorless wax that is prized for its ability to moisturize skin and act as an emulsifier in creams and lotions. Lanolin and its derivatives appear in lip balms, nipple creams for breastfeeding, shoe polish, rust-prevention coatings, and even as a processing aid in the textile industry. For people with lanolin allergies, which affect a small percentage of the population, this ubiquity can be a hidden trigger in products that do not obviously advertise their animal origins.

Biofuel and Renewable Energy

Animal fats have found a growing market as feedstock for biofuels. Tallow and used cooking oil (sometimes called yellow grease) can be chemically converted into hydroprocessed renewable diesel and jet fuel, offering a way to displace petroleum-based fuels. Life-cycle analyses have calculated the greenhouse gas emissions and production costs associated with these fuels, and tallow-based biofuels generally come out favorably compared to fossil alternatives.¹⁴ Process simulations have explored blending soybean oil with animal tallow to optimize the mix of hydrocarbons produced, finding that certain ratios can improve selectivity for kerosene-range fuels while reducing hydrogen consumption during refining.¹⁵

Biogas is another energy pathway. Slaughterhouse byproducts can be broken down through anaerobic digestion to produce methane. Different materials vary widely in their energy potential: pure fat yields the most methane per kilogram, while meat-and-bone flour produces the least among the tested fractions. Raw slaughterhouse waste as a mixed stream still delivers a meaningful methane yield.¹⁶ As the aviation and shipping industries face pressure to decarbonize, animal fats are increasingly competing with vegetable oils for space in the renewable fuels pipeline.

Fertilizers and Soil Amendments

Blood meal, bone meal, feather meal, and composted manure are all animal byproducts used in agriculture. These materials are rich in nitrogen, phosphorus, and calcium, making them useful as organic fertilizers. Blood meal, for instance, typically contains around 12 to 13 percent nitrogen and breaks down relatively quickly in soil. Research on organic rice production found that pelletized fertilizers made from blood, meat, and feather meal released most of their mineralized nitrogen within the first 53 days after planting, timing that aligns well with when rice plants need it most.¹⁷

For organic farmers, who cannot use synthetic nitrogen fertilizers, animal-derived amendments are often among the most concentrated and reliable nitrogen sources available. Bone meal serves a different niche: it is slow-release and rich in phosphorus, making it useful for root development and flowering. These products close a nutrient loop, returning minerals from the slaughter process back to cropland rather than sending them to a landfill.

Safety Concerns and Regulatory Boundaries

Not all animal byproducts are safe to recycle. The most prominent example involves bovine spongiform encephalopathy, commonly known as mad cow disease. The misfolded proteins that cause BSE concentrate in certain nervous-system tissues of cattle, collectively labeled “specified risk materials” or SRMs. Strict bans require that these tissues be isolated and destroyed rather than entering the rendering stream, an expensive obligation for processing companies.¹⁸ In most countries, SRMs from cattle over a certain age must be incinerated or disposed of in approved facilities, and their use in any animal feed is prohibited.

These regulations reshaped the rendering industry in the 1990s and 2000s. Before the BSE crisis, it was common practice to feed rendered cattle protein back to cattle, a practice that amplified the disease. Feed bans broke that cycle, and today the rules differ by country but generally restrict which species’ byproducts can be fed to which other species. The European Union maintains some of the strictest rules, while other regions have adopted varying degrees of precaution.

The Environmental Case for Using Byproducts

Rendering has a surprisingly strong environmental profile compared to the alternatives. A comparative review found that rendering plant operations emit roughly a quarter of the carbon dioxide that would be released if the same quantity of meat byproducts decomposed aerobically in a landfill or compost pile.⁵ Composting, while popular in some settings, actually releases significant amounts of methane and nitrous oxide, both potent greenhouse gases, and achieving reliable pathogen destruction in a compost pile is harder than in a controlled rendering cooker.

That said, newer technologies are drawing attention. Anaerobic digestion, if done in sealed systems, produces low greenhouse gas emissions and generates usable biogas. Some researchers have argued that alternative disposal technologies may offer a lower environmental footprint than traditional rendering in certain contexts, particularly for on-farm carcass disposal.¹⁹ The tradeoff is that large-scale experience with digesting meat byproducts remains limited, and regulations have not fully caught up.

Consumer Perception and the “Ick” Factor

One of the biggest barriers to expanding the use of animal byproducts, particularly in human food, is disgust. Research across European countries has found that food disgust sensitivity is a significant barrier to people’s willingness to eat animal byproducts like organ meats or blood-based foods.²⁰ At the same time, social norms and culinary traditions can push in the other direction. In cultures where offal dishes are common and celebrated, the same ingredients provoke no hesitation.

When byproduct-derived ingredients are used in processed foods rather than served whole, consumer attitudes shift. Focus groups across Italy, Germany, Romania, and Norway found that most participants were actually open to buying bakery, meat, or dairy products enriched with nutrients extracted from food industry byproducts. Their main motivations were health benefits and reducing food waste. Their main concerns were potential new allergens and the possibility that byproduct-derived ingredients might concentrate contaminants like pesticides.²¹ This gap between “I would not eat a kidney” and “I would eat bread enriched with protein from meat processing” is something food companies are actively trying to navigate.

Insect Byproducts as an Emerging Frontier

The concept of animal byproducts is expanding beyond traditional livestock. As insect farming grows, so does the question of what to do with the leftover material after the edible protein is extracted. Mealworm shells and cricket exoskeletons, for example, are rich in chitin, a structural polysaccharide that can be processed into chitosan, a compound with applications in water treatment, wound dressings, food preservation, and biodegradable packaging. Chitin has traditionally been sourced from shrimp and crab shells, but insect biomass and its processing residues are now being explored as a more sustainable alternative.²²

Research on mealworm processing residues has confirmed that the leftover biomass from adult beetles contains a high chitin fraction and low mineral content, making it well suited for biopolymer recovery. Enzyme-assisted extraction methods have been optimized to pull chitin and chitosan from these residues efficiently, supporting what researchers describe as a circular biorefinery approach where nothing from the insect farm goes to waste.²³ Whether insect-derived chitin can scale up to compete with crustacean sources remains an open question, but the principle mirrors what the traditional rendering industry has practiced for decades: finding value in what would otherwise be thrown away.