Cows are herbivores, so a cow that eats a small amount of meat by accident will likely be fine in the short term. Their digestive system isn’t designed for it, but it won’t poison them on the spot. The real danger is what happened when the livestock industry routinely fed cattle processed meat-and-bone meal made from other cattle: it caused bovine spongiform encephalopathy, better known as mad cow disease, one of the most alarming food safety crises in modern history.
Why a Cow’s Digestive System Isn’t Built for Meat
Cattle have a four-chambered stomach designed to break down tough plant fibers through fermentation. Billions of specialized microbes in the rumen (the largest chamber) convert cellulose from grass and grain into nutrients the cow can absorb. Meat protein doesn’t go through this process efficiently. A cow that nibbles on a piece of meat, a dead bird, or an afterbirth (which does happen occasionally on farms) can digest some of the protein, but it’s not getting meaningful nutrition from it.
In small, one-off amounts, meat doesn’t cause immediate illness. The cow’s system simply processes what it can and passes the rest. The serious problems begin when meat-based protein becomes a regular part of the diet, which is exactly what happened in industrial cattle farming for decades before regulators stepped in.
How Feeding Meat to Cows Created Mad Cow Disease
Starting in the 1980s, the cattle industry widely used meat-and-bone meal as a cheap protein supplement in feed. This rendered product was made from the carcasses of dead cattle and other animals, ground up and processed at high temperatures. The practice seemed efficient: it boosted growth and recycled waste. But it turned cattle into unwitting cannibals, and it unleashed a devastating chain of infection.
Some of those rendered carcasses contained prions, which are misfolded proteins that act as infectious agents. Unlike bacteria or viruses, prions are extraordinarily durable. Standard rendering processes, which involve high heat and pressure, don’t destroy them. When a healthy cow ate feed containing prion-contaminated meat-and-bone meal, those prions accumulated in its brain and nervous system, causing BSE.
The disease spread in a vicious cycle. Infected cows were slaughtered, rendered into more meat-and-bone meal, and fed back to other cattle. The United Kingdom saw the worst of it, with over 180,000 confirmed cases during the peak of the epidemic in the late 1980s and early 1990s.
What BSE Does to a Cow
BSE has a long incubation period, typically four to six years. A cow can be infected and show no signs for years. When symptoms finally appear, they progress quickly and are always fatal. There is no treatment and no cure.
The first signs are usually behavioral. An infected cow becomes nervous, aggressive, or unusually fearful. This is why the disease earned the name “mad cow disease.” As it progresses, the cow loses coordination, has trouble walking, and struggles to stand up. The prions are literally creating sponge-like holes in the brain tissue, destroying it from the inside. Once symptoms start, the animal typically dies within weeks to months.
The Human Cost: Variant CJD
The reason mad cow disease became a global crisis wasn’t just the cattle. People who ate beef contaminated with BSE-infected tissue developed a fatal brain disease called variant Creutzfeldt-Jakob disease (vCJD). The CDC states there is strong evidence vCJD is caused when people eat meat from BSE-infected cows.
The incubation period in humans is also disturbingly long. Scientists believe people were exposed to contaminated beef in the mid-1980s, and vCJD cases started appearing about a decade later. The disease causes rapid mental deterioration, psychiatric symptoms, and death, usually within about 13 months of symptom onset. Over 230 people worldwide have died from vCJD, the vast majority in the U.K.
Feed Bans That Changed the Industry
Governments responded with sweeping regulations that fundamentally changed how cattle are fed. In the U.S., the FDA banned feeding mammalian protein to cattle and other ruminants in 1997. A second, stricter rule followed, prohibiting high-risk cattle materials from being used in feed for any animal species, not just ruminants. The banned materials include:
- Entire carcasses of any cattle that tested positive for BSE
- Brains and spinal cords from cattle 30 months of age and older
- Carcasses of cattle not inspected and passed for human consumption (unless the animal is under 30 months old or the brain and spinal cord have been removed)
- Certain rendered fats (tallow) from BSE-positive cattle or from prohibited materials if they contain more than 0.15% insoluble impurities
These policies, combined with the removal of infectious tissues like brain and spinal cord from the human food supply, led to a dramatic decline in BSE cases worldwide. The feed bans broke the cycle of cow-to-cow transmission that had fueled the epidemic.
How Cattle Are Monitored Today
The USDA’s surveillance program currently tests approximately 25,000 cattle per year, targeting the populations where BSE is most likely to appear: older cattle, animals that died on the farm, and those showing neurological symptoms. The World Organisation for Animal Health classifies countries into three BSE risk categories (negligible, controlled, or undetermined), and the U.S. recognizes these designations when making import decisions.
BSE still exists at extremely low levels. Rare “atypical” cases pop up sporadically in older cattle around the world, believed to occur naturally rather than through contaminated feed. But the large-scale epidemic driven by feeding meat to cows is effectively over, a direct result of the feed bans put in place in the late 1990s and 2000s.
The Short Answer
A single cow eating a scrap of meat on a pasture is unlikely to suffer any harm beyond mild digestive inefficiency. But when the practice was industrialized, when millions of cattle were routinely fed the rendered remains of other cattle, it created the conditions for a prion disease that killed animals, killed people, and permanently changed food safety regulations around the world. The lesson was expensive: cows are herbivores, and treating them otherwise carries consequences far beyond an upset stomach.