Chipotle, the world’s greatest fast-food chain, is backtracking on its commitment to serving only beef raised without antibiotics. Excerpt:

The burrito seller will use meat from cattle treated with antibiotics because of an illness, which previously wasn’t permitted to be sold in its restaurants, Chris Arnold, a spokesman for Denver-based Chipotle, said in an email. The company still won’t use beef from animals that had been given antibiotics to prevent disease and promote weight gain, he said.

The change in Chipotle’s practices comes as U.S. beef production is projected to plunge to a 21-year low next year, threatening higher costs and making it tougher for the restaurant chain to obtain enough meat.

“The change was really rooted in the belief that it’s not the use of antibiotics for the treatment of illness that is the problem,” Arnold said later in an interview. “The problem is the copious amount of antibiotics that are used to promote growth.”

While Arnold said the motivation for the change isn’t to increase its supply of steak, Chipotle hasn’t been able to get enough naturally raised beef to meet customer demand. This year, about 80 percent to 85 percent of the beef sold at Chipotle’s more than 1,500 stores has been naturally raised, compared with almost 100 percent last year, Arnold said.

“Every year we need 20 to 25 percent more of everything than we did the year before, and the beef supply isn’t keeping up as well,” he said.

Too many people want naturally-raised beef to meet the demand? That’s a good problem to have. I think.