A cyberattack on JBS SA, the largest meat producer globally, has forced the shutdown of some of world’s largest slaughterhouses, and there are signs that the closures are spreading. JBS’s five biggest beef plants in the U.S. -- which altogether handle 22,500 cattle a day -- have halted processing following a weekend attack on the company’s computer networks, according to JBS posts on Facebook, labor unions and employees. Those outages alone have wiped out nearly a fifth of America’s production. Slaughter operations across Australia were also down, according to a trade group. One of Canada’s largest beef plants was idled...