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How a Pile Up of Dead Cows Led to the Discovery of What’s In Pet Food. And It’s Much Worse Than You Think.

“Fresno County declares emergency as cow carcasses pile up. Plant to temporarily close” and “Merced County declares an emergency, as cattle carcasses pile up from rendering plant issue.”

It’s just the sort of headlines I dread. Even though I know what the rendering industry does – which is recycling dead livestock, animal by-products, expired meat and used cooking oil – I began to wonder with a morbid fascination what does a cow looks like after it’s lain outside after – say – a week or two. I mean really look like. Up close.


It started when a boiler started leaking at a livestock rendering plant in Fresno County, causing it to work inefficiently. The rendering plant, Baker Commodities, which covers the Southwest Region of the United States, and the only one of its size in the Central San Joaquin Valley, was forced to shut down Feb 21 while they fixed their equipment. And that’s when the carcasses began piling up, and the company was forced to stop picking up dead cows, bulls, and horses. By the time the rendering plant resumed operations on March 6, animals had been out there for ten days.


Typically, the rendering process involves first removing the animals’ hides at Baker Commodities Hanford facility and then hauling the rest of the carcasses to its Kerman facility, where the boiler broke down, to complete the rendering process. But once an animal has decayed past a certain point – after ten days, for example – removing the skins becomes problematic, and the entire body must be rendered whole. While in practice, horses should be separated from the other animals, particularly as they may have been euthanized with pentobarbital when the horses decay past the point of being a solid mass, separating them from other animals becomes impossible.


Then Darling Ingredients, Inc., the only other livestock renderer in Fresno County, reported mechanical failures forcing the company to stop its rendering operation on Feb 28. When the only two area livestock rendering facilities suffering malfunctions in the San Joaquin Valley, livestock owners who depend upon such plants to dispose of deceased animals were in a panic. While equipment issues at both plants impacted the area, it was the Darling Ingredients plant malfunction that triggered the local emergency. Darling Ingredient’s plant in Fresno is typically capable of process around 850,000 pounds of bones, fat, and other refuse a day, even though Darling’s facility was back up and running a few days later, the backlog of animal carcasses persists. If the accumulated carcasses are not mitigated by the local emergency’s March 31 deadline, it may be extended. However, the backlog is expected to be cleared within a few weeks.


Fortunately, the local emergency allowed county landfills to temporarily receive dead livestock. Some landfills have a license to receive livestock mortalities regularly or when an emergency proclamation is made. The situation, however, shows how fragile the system is for dairymen who are legally unable to bury or burn deceased livestock. This is why farmers are utterly dependent on renderers who perform an invaluable service to the community. And it’s not just farmers and the meat and poultry industry who rely on renderers, it’s supermarket chains who dispose of expired grocery store meat, and food chains who need to dispose of used cooking oil.


Without renderers – and it’s hard to imagine the picture – the U.S. would be overwhelmed with an unimaginable volume of animal mortalities and animal by-products. There is no question renderers provide an essential service: disposing of millions of pounds of dead animals every day. No one can question the necessity of such an industry, in fact, most people use rendered products every day, they just don’t realize it, because it is used in so many things: cosmetics, candles, detergents, gelatin, lard, soaps, even marshmallows. And of course pet food and animal feed.


Not many consumers are aware that most pet foods on the market contain rendered ingredients, including pet food ingredients manufactured by Darling Ingredients, and Baker Commodities’ protein meal and animal fats. It’s pretty hard to walk down the aisle of a grocery store and avoid buying a pet food product that wasn’t made using some rendered product in it. After all, the pet food industry is the largest user of rendered fats and proteins.

Perhaps it was just bad luck or a bad two weeks for farmers, maybe dealing with dead animals is an inconvenience that farmers and renderers have to deal with daily as part of doing business. But for consumers who buy pet food that contains rendered material, the story illustrates how consumers might want to be aware of what happens on the days when everything doesn’t go as planned at the local rendering plant. Consumers should be aware that it is not just possible that bad things happen, but that they do.


The National Renderers Association’s guidance for rendering plants certifying in the Rendering Code of Practice and Animal Feed Industry Association’s FSC36 Safe Feed/Safe Food program outline how processing filthy, putrid, and decomposing animals is an acceptable means of turning the material into useful feed ingredients for animals:

Decomposition of animal tissues begins the moment slaughter takes place, and some time is needed to get these materials into the rendering process. Decomposition is not always a negative for product quality and food safety. The rendering process effectively “re-sets the clock” by processing raw materials including offal, outdated meat, and fallen animals that may be deemed filthy, putrid, or decomposed substances with respect to human food into safe, wholesome, and useful feed ingredients for animals.

Which, oddly, is in direct conflict with the Federal Food Drug and Cosmetic Act, 21 U.S. Code § 342 Adulterated food that states a food shall be deemed to be adulterated (poisonous, insanitary, etc.):

“…if it consists in whole or in part of any filthy, putrid, or decomposed substance, or if it is otherwise unfit for food; or if it has been prepared, packed, or held under insanitary conditions whereby it may have become contaminated with filth, or whereby it may have been rendered injurious to health; or if it is, in whole or in part, the product of a diseased animal or of an animal which has died otherwise than by slaughter.”

When searching for a good illustration of the process of decomposition – of what a ten-day-old cow might look like, for example – I came across the Australian Museum’s Department of Natural Science’s study of the stages of decomposition carried out on a piglet. The website explains:

Decomposition of a corpse is a continual process that can take from weeks to years, depending on the environment. Below we have divided the process into stages, which are characterised by particular physical conditions of the corpse and the presence of particular animals.
To illustrate the process of decomposition, we use the piglet as the model corpse. Piglets are used because a 40 kg pig resembles a human body in its fat distribution, cover of hair and ability to attract insects. These factors make pigs the next best things to humans when it comes to understanding the process of decay of the human body. The pigs in this website are newborn piglets (weighing about 1.5 kg) that have been accidentally crushed by their mothers – a key cause of death of piglets. Their bodies have been donated to science.

Please note – this set of images contain strong graphic references.


newborn piglets (weighing about 1.5 kg)

Newborn piglets (weighing about 1.5 kg)

STAGES OF DECOMPOSITION | Stage 2: Initial decay – 0 to 3 days after death

Decomposition of pig, Stage 2: Initial decay State of decay Although the body shortly after death appears fresh from the outside, the bacteria that before death were feeding on the contents of the intestine begin to digest the intestine itself. They eventually break out of the intestine and start digesting the surrounding internal organs. The body's own digestive enzymes (normally in the intestine) also spread through the body, contributing to its decomposition. On an even smaller scale, enzymes inside individual cells are released when the cell dies. These enzymes break down the cell and its connections with other cells. Insect activity From the moment of death flies are attracted to bodies. Without the normal defences of a living animal, blowflies and house flies are able to lay eggs around wounds and natural body openings (mouth, nose, eyes, anus, genitalia). These eggs hatch and move into the body, often within 24 hours. The life cycle of a fly from egg to maggot to fly takes from two to three weeks. It can take considerably longer at low temperatures. Image: R Major © Australian Museum

Stage 2: Initial decay

stage one of decay dead pig fly

Stage 2: Initial decay – 0 to 3 days after death; Fly attracted to the dead pig.

Fly eggs on dead pig Image: R. Major © Australian Museum

Stage 2: Initial decay – 0 to 3 days after death; Fly eggs on dead pig

Fly larvae - Maggots, First-instar. The larva, or maggot, is the main feeding stage of the fly. On hatching, first-instar larvae are roughly 2 mm long, growing to about 5 mm before shedding their skin. Image: R. Major © Australian Museum

Stage 2: Initial decay – 0 to 3 days after death; Fly larvae – Maggots, First-instar

STAGES OF DECOMPOSITION | Stage 3: Putrefaction – 4 to 10 days after death

Decomposition Stage 3 Putrefaction 4 to 10 days after death

Stage 3: Putrefaction – 4 to 10 days after death

Stage 3: Putrefaction - 4 to 10 days after death Image: R. Major © Australian Museum

Stage 3: Putrefaction – 4 to 10 days after death

Stage 3: Putrefaction - 4 to 10 days after death Image: R. Major © Australian Museum

Stage 3: Putrefaction – 4 to 10 days after death

STAGES OF DECOMPOSITION | Stage 4: Black putrefaction – 10 to 20 days after death
Stage 4: Black putrefaction - 10 to 20 days after death Image: R. Major © Australian Museum

Stage 4: Black putrefaction – 10 to 20 days after death

Stage 4: Black putrefaction - 10 to 20 days after death Image: R. Major © Australian Museum

Stage 4: Black putrefaction – 10 to 20 days after death

Stage 4: Black putrefaction - 10 to 20 days after death Image: R. Major © Australian Museum

Stage 4: Black putrefaction – 10 to 20 days after death

I did not include the latter stages of decomposition as it seemed unlikely that a renderer would ever have to cope with corpses 20 days after its death.


To some consumers, it might simply be a matter of aesthetics, or it might be because of the perceived quality of the fats and proteins. To others, it may be more worrisome. It may be that rendered ingredients are made from diseased, inedible meat and poultry, and the odd horses. Or maybe they worry about pentobarbital or dioxins in rendered material. In which case, consumers may wish to avoid buying pet food with animal-fat, animal by-product, animal-digest, meat, and bone meal because those are likely to be from a renderer. 

The question consumers should ask themselves is: Is what you see on the pet food package or can differ from what you perceive rendered ingredients to be? Are the images on the packages and cans of pet food contradictory to the images of inedible meat and poultry – the witch’s brew of feet, heads, stomachs, intestines, hooves, spinal cords, tails, grease, feathers, and bones? Do you feel betrayed, or robbed of your choice because of misleading advertising claims?

I’d like to hear your thoughts.


Stages of Decomposition, Museum of Natural History and Sciences Australia

Dar Pro Ingredients, a division of Darling Ingredients Inc., animal and pet food ingredients

Baker Commodities, Inc. protein meals, and feeding fats

Encyclopedia of Sh*t You Don’t Want to Know About, But Should: The Pet Food Industry Edition

A Rare Look Inside a Rendering Plant

Eating the Dead: Pet Food Only a Zombie Could Love; The Circular Madness of Upcycling Dead, Dying, and Diseased Animals into Food for Animals

Pet Food Industry’s Darkest Secret: Chemically Denatured Condemned and Inedible Material

dog cat poisoned pets safe food warnings news recalls alerts

Poisoned Pets | Pet Food Safety News remains free (and ad-free) and takes me many, many hours of laborious work to research and write, and thousands of dollars a year to sustain. Help keep Poisoned Pets alive by making a donation. Thank you.




Mollie Morrissette

Mollie Morrissette, the author of Poisoned Pets, is an animal food safety expert and consumer advisor. Help support her work by making a donation today.

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