CJD in humans has an incubation period of 10 to 40 years. Thus, by the time symptoms of BSE appear, many cows are likely to be carrying the infection silently. TSE diseases are characterized by a long incubation period, and they are always fatal. Furthermore, the infectious agent is incredibly resistant to deactivation. Cooking infected meat, or even rendering it at high temperature, does not completely eliminate its infectivity.
Animals get TSEs by eating infected animals or parts of infected animals, especially nerve tissues.
TSE diseases have now been identified in sheep, pigs, goats, cattle, deer, elk, mink, mice, hamsters, guinea pigs, domestic cats, puma, cheetah, eland, kudu, Arabian oryx, myland, marmosets, macaques, chimpanzees and humans. But that is not what the FDA has done. Ruminants are animals that chew their cuds, including cattle, sheep, goats, deer and elk. Mink are included in the ban because they can get a TSE similar to mad cow disease. FDA is still allowing the feeding of pigs to other animals, and the feeding of blood and gelatin from rendering plants to all animals.