Analysts claim the British "Mad cow disease" has been caused by cows which have eaten what?

The crisis surrounding Bovine Spongiform Encephalopathy (BSE), as the disease is formally known, was traced to a cost-cutting practice in the cattle industry. For years, cattle feed was supplemented with meat-and-bone meal (MBM), a high-protein powder created by rendering the carcasses of other livestock, including sheep and other cows. This practice effectively forced naturally herbivorous cows into a form of cannibalism, creating a pathway for disease to spread rapidly through the food chain.

The infectious agent responsible was not a virus or bacteria, but a misshapen protein called a prion. When ingested, these prions cause a chain reaction in the host's brain, forcing normal proteins to misfold and creating sponge-like holes in the neural tissue, leading to the devastating neurological symptoms. The leading theory suggests the prions originated in sheep infected with a similar disease called scrapie, which then crossed the species barrier to cattle through the MBM feed.

The situation became a major public health emergency when scientists discovered that humans could contract a fatal variant, Creutzfeldt-Jakob disease, by eating contaminated beef. This link led to massive culls of British cattle and sweeping changes in agricultural regulations worldwide, including strict bans on the use of rendered animal remains in feed for livestock.