By Fabiana Batista, Michael Hirtzer and Elizabeth Elkin | Bloomberg

A cyberattack on JBS SA, the largest meat producer globally, has forced the shutdown of some of the 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 for a second day.

It’s unclear exactly how many plants have been affected by the attack globally as JBS has yet to release details that granular. The prospect of more extensive shutdowns around the world is already upending agricultural markets and raising concerns about food security as hackers increasingly target critical infrastructure. In the U.S., JBS accounts for about a quarter of all beef capacity and roughly a fifth of all pork capacity. Livestock futures slumped while pork prices rose.

The Brazilian meat giant shut its North American and Australian computer networks after an organized assault on Sunday on some of its servers, the company said by email. Without commenting on operations at its plants, JBS said the incident may delay certain transactions with customers and suppliers.

“Retailers and beef processors are coming from a long weekend and need to catch up with orders,” Steiner Consulting Group said in its Daily Livestock Report. “If they suddenly get a call saying that product may not deliver tomorrow or this week, it will create very significant challenges in keeping plants in operation and the retail case stocked up.”

JBS closed meat processing facilities in Utah, Texas, Wisconsin and Nebraska and canceled shifts at plants in Iowa and Colorado on Tuesday, according to union officials and employees. Union Facebook posts also said some kill and fabrication shifts in the U.S. have also been canceled. Pork and chicken facilities across the nation are also…