Bovine spongiform encephalopathy (BSE), otherwise known as mad cow disease, is a fatal neurogenerative disease in cattle that causes a spongy degeneration of the brain and spinal cord. BSE is caused by a misfolded protein known as a prion. It is thought that normal prion protein changed, for reasons unknown, into a harmful, pathogenic form, which damages the cow's CNS.

BSE was first identified in the 1970s, which is thought to have originated from feeding cattle feed containing parts of other cows or scrapie-infected sheep meat (in the form of meat-and-bone meal). Scrapie is a prion disease of sheep.

Statistics
BSE is epizootic in the United Kingdom, and by the end of 2010 had more than 184,500 cases of BSE in more than 35,000 herds.

Incubation period
BSE has a long incubation period, and can take anywhere from 30 months to 8 years to develop in cattle. It usually affects adult cattle between four and five years of age.