Mad cow disease is a progressive brainwasting disease that is always fatal. It is caused by a type of defective protein known as a prion and cannot be cured. The factory farming practices of feeding animals on the nervous tissue of other animals first caused the ballooning spread of mad cow disease and created the current crisis. When it became clear what had happened, many countries banned feeding the tissue of ruminants (cows, sheep and goats) to other ruminants.