Prions are normal. Without DNA, reproduction should not be possible. However, it is now becoming widely accepted that prions do reproduce themselves and do cause disease. The abnormal prions also cause other nearby prions to become folded into the same shape, thus creating more abnormal prions by a domino effect. Thus animals and humans can be carrying an infectious prion disease for months or years without showing any symptoms.
Ruminants are animals that chew their cuds, including cattle, sheep, goats, deer and elk.
Mink are included in the FDA's ban because they can get a TSE similar to mad cow disease. When cows, pigs, and chickens are slaughtered, much of the animal cannot be used for food and is sent to a rendering plant to be ground up, boiled down, dried to the consistency of brown sugar and sold as feed for cows, pigs, chickens, and pets. The FDA ban also allows blood and gelatin derived from ruminants to be fed to other ruminants. In the U.S., many newborn calves are fed a high-protein diet consisting mainly of dried blood. Scientists on both sides of the controversy agree that mad cow disease probably developed in Britain in one of two ways.