How Now Brown Cow

Fact: Mad Cow Disease was caused by cows eating other cows.

Rather than the setup for a creepy horror film it’s cold hard fact: it was cow cannibalism that set off the Mad Cow Disease epidemic in the UK.

‘Mad Cow Disease’, otherwise known as BSE (or Bovine Spongiform Encephalopathy) is quite a unique disease. It’s infectious, but rather than being caused by a familiar face like a virus or bacteria, it’s caused by something called a prion.


A prion is a misfolded protein that can make copies of itself, even though it isn’t a living thing. In the case of Mad Cow Disease, the protein responsible was called PrPC. The normal form of PrPC is present on nerves and in the brain of healthy cows, but it can misfold into a different structure – called PrPSc – which is a prion and causes disease. This means that when a misfolded PrPSc protein meets a normal PrPC protein in the body, it causes the PrPC to change shape and become PrPSc itself. This new PrPSc protein can then go off and make more copies of itself, which is how the disease spreads.


But how did the first PrPSc get misfolded in the first place? Mad Cow Disease is closely related to an older disease called scrapie, which affects sheep and is caused by a prion very similar to PrPSc. In 1986, farms used to feed cows with something called ‘meat & bone meal’, which is the ground up remains of other animals. Some of those animals were sheep that were infected with scrapie, which then allowed the prion to infect cows.

However, the spread of the disease in cows was down to a second practice – dead cows were ground up and fed to the living (much like how things work in The Matrix). This meant that cows infected with Mad Cow Disease were recycled into the food chain, and spread the prion far and wide across the UK’s cattle farms.

So there you have it – cannibalism is bad. Who’d have thought it. It’s worth mentioning that, contrary to my opening statement, mad cows is indeed also the setup for a creepy horror film. Check out straight-to-DVD release “Isolation” for the ‘mad cow’ film you never knew you wanted.

‘Another one of Mr Shaunak’s Little Bites of Science’
Image under Creative Commons license

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