It simply makes animals much less productive. Mad-cow disease, on the other hand, is not contagious but has been linked to fatalities of people who eat the infected meat. The US may well serve as an important model for how government, private veterinarians, and farmers can prevent outbreaks of such diseases. Neither of its neighbors has been infected. And it is less susceptible to mad-cow disease because it never supported an extensive sheep industry the way Britain has.
Scientists believe mad-cow disease spread through such feed.
Still, the US has taken strong preventative steps. In 1989, it banned all livestock and related products from countries with confirmed mad-cow cases. It has followed up with bans on animal-based feed and an aggressive program to test suspect cows. Such an outbreak would prove even more difficult for the US, where calves typically raised in, say, Florida are shipped more than 1,000 miles to large feedlots in Texas and elsewhere to get fattened up. On the other hand, British authorities believe the disease was introduced not by a large corporate farm but by a small and, by some accounts, squalid hog operation in the north of England.