Inedible animal food refers to animal parts, tissues, and byproducts that are not approved or intended for human consumption but are instead processed into products like pet food, livestock feed, fertilizers, and industrial materials. The term covers everything from parts that humans physically cannot eat (hooves, horns, hides, feathers) to parts that regulators have banned from the human food supply for safety reasons, as well as meat that failed inspection or was never intended for your plate.
How “Inedible” Is Officially Defined
Under federal regulations, “inedible” has a broader meaning than you might expect. For meat products, it covers three categories: meat that is adulterated (contaminated or spoiled), uninspected (never examined by a federal inspector), or simply not intended for human consumption. For poultry, the definition includes any carcass or part that is either naturally inedible or has been rendered unfit for human food through contamination or deliberate denaturing.
The regulations also draw a distinction between parts that are “naturally inedible” and parts that are “not for use as human food.” Naturally inedible items are things humans physically cannot eat: hooves, horns, hides, feathers, and poultry entrails. Parts banned from human food for safety or regulatory reasons include lungs, thyroid glands, lactating mammary glands, and certain reproductive organs. These parts may be biologically possible to consume, but federal rules keep them out of the human food chain.
One important category involves cattle tissues banned specifically because of mad cow disease (BSE) risk. The brain, skull, eyes, spinal cord, and vertebral column from cattle 30 months of age and older are classified as specified risk materials. The tonsils and a section of the small intestine from all cattle, regardless of age, also fall into this category. These tissues are explicitly prohibited from human food.
How Inedible Material Is Kept Out of Human Food
To prevent inedible animal products from accidentally entering the human food supply, regulators require a process called denaturing. This involves treating condemned or inedible material with agents that give it a distinctive color, odor, or taste so it cannot be confused with food. Common denaturing agents include food-grade green and blue dyes, finely powdered charcoal, crude carbolic acid, and even oil of citronella mixed with liquid detergent. For inedible rendered fats, charcoal must be mixed in at a minimum concentration and must remain visibly suspended in the liquid fat.
The rules get surprisingly specific. Tripe, for example, is denatured by dipping it in tannic acid followed by a yellow dye bath. Cuts of meat denatured with charcoal must reach a minimum level of darkness, verified against an official reference diagram. The goal is simple: make the material look, smell, or taste so obviously wrong that no one could mistake it for something you’d eat.
What Happens to Inedible Animal Material
The vast majority of inedible animal material goes through rendering, a process that uses heat and pressure to break down tissues into two broad categories: fats (like tallow and grease) and protein meals. In 2022, the U.S. produced 10.7 million metric tons of rendered products total, split roughly into 6 million metric tons of fats and greases and 4.7 million metric tons of protein meals. Inedible tallow alone accounted for nearly 1.8 million metric tons.
Rendering typically involves cooking raw material (a mix of soft organ tissues, industrial bones, and sometimes whole carcasses of animals that died on farms) at high temperatures, then separating the fat from the solid protein. The solids are dried and ground into meals with uniform particle sizes. These products then flow into several industries.
Pet Food and Livestock Feed
Pet food is one of the most visible destinations for inedible animal material. Ingredients labeled “meat meal” on a pet food bag are rendered mammal tissues, ground into uniform particles, excluding hair, hooves, horns, hides, manure, and stomach contents. “Meat byproducts” refers to non-rendered clean parts like lungs, spleens, kidneys, brains, livers, blood, bone, and intestines. While the USDA does not allow lungs or udders in human food, these parts can be safe and nutritious for dogs and cats.
Livestock feed also absorbs large quantities of rendered protein meals and fats, though regulations restrict feeding ruminant-derived protein back to other ruminants to prevent BSE transmission.
Fertilizers
Blood meal and bone meal are two common garden fertilizers made from inedible slaughterhouse byproducts. Blood meal is dried animal blood, high in nitrogen, and water-soluble enough to apply as a liquid feed. Bone meal is made from steamed, finely ground animal bones and provides calcium, phosphorus, and trace minerals like magnesium, zinc, and iron. Both are slow-release fertilizers valued in organic gardening for improving soil health and supporting root development.
Industrial and Pharmaceutical Uses
Inedible tallow and other rendered fats feed into the production of soaps, candles, lubricants, and increasingly, biofuels. Certain glands and organs are set aside specifically for pharmaceutical or “organo-therapeutic” purposes and must be labeled accordingly. These products never enter the food supply but serve as raw materials for medical and technical applications.
Why It Matters Economically
Rendering transforms what would otherwise be a massive waste disposal problem into a multibillion-dollar supply chain. In 2022, rendered fats like inedible tallow traded at roughly $1,649 per metric ton, while protein meals like meat and bone meal sold for $1,035 to $1,181 per metric ton depending on the animal source. Blood meal, feather meal, and poultry byproduct meal each command their own market prices, with blood meal reaching as high as $1,436 per metric ton. The industry processes roughly 40 to 50 percent of every slaughtered animal’s weight that doesn’t end up as retail meat, converting it into marketable products rather than landfill waste.