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

The devastating outbreak of "Mad Cow Disease," scientifically known as Bovine Spongiform Encephalopathy (BSE), in Britain during the 1980s and 1990s was primarily attributed to a change in cattle feeding practices. Instead of their natural vegetarian diet, cows were given feed that included processed animal by-products, specifically meat-and-bone meal (MBM). This MBM contained the remains of other animals, including sheep infected with scrapie, a similar prion disease.

The infectious agent responsible for BSE is a misfolded protein called a prion. While scrapie had long existed in sheep, the rendering process used to create MBM was altered in the UK, reportedly at a time when energy costs increased. This change in the rendering process, which involved lower temperatures and less solvent extraction, was insufficient to inactivate the scrapie prion present in the infected animal remains. Consequently, these prions were able to survive in the feed and infect the cattle that consumed them, leading to the widespread emergence of BSE.

The consumption of BSE-infected beef products by humans then led to a new, fatal neurological condition called variant Creutzfeldt-Jakob disease (vCJD). This tragic link highlighted the critical importance of feed regulations and animal health surveillance. Strict controls were subsequently implemented to prevent specified risk materials, such as brain and spinal cord tissue, from entering the human and animal food chains, drastically reducing the incidence of both BSE in cattle and vCJD in humans.