Following years of debate, the U.S. Food and Drug Administration has curtailed the use of antibiotics in livestock production.

Effective January 1 this year, American farmers can no longer use antibiotics to promote faster growth in animals.

Based on the new rules, antibiotics can be utilized only for disease prevention, which will be subject to oversight by veterinarians.

The tightening of rules on the so-called “medically important antimicrobials” came decades after antibiotics have been routinely fed to animals so they can grow faster and combat disease.

It’s a practice driven by economics, mainly to meet the American appetite for cheap meat.

Public health advocates have warned that this practice produces antibiotic resistant bacteria in animals, which can later cause adverse health effects on humans.

This is the backdrop of a new book by Maryn McKenna, an American journalist who specializes in public health and food policy.

In Big Chicken, McKenna chronicles the use of antibiotics in U.S. agriculture, and how modern food production became a threat to human health.

In an interview with Wired magazine, McKenna said the farmers were once feeding around 63,000 tons of antibiotics to livestock.

“I had the impression that concerns over casually using antibiotics in agriculture were a pretty new thing," she told the publication. "So I was shocked to learn that warnings about its unintended consequences go back to the very start of these practices.

“Over and over again, in every decade since 1948, somebody stepped up and said, ‘We are making a mistake. This is going to undermine the action of antibiotics, this is going to make people sick,’ " McKenna continued in her Wired interview. "And whoever that person was they were dismissed and that warning wasn’t heard. Some of the scientists in the company that started this—did the first experiments, sold the first growth promoters to chicken farmers—those veterinarians said, ‘Hey, we shouldn’t do this,’ and their bosses overruled them.”

According to the Georgia-based Centres for Disease Control and Prevention, antibiotics should be “used responsibly in both humans and animals because both uses help bring about the development, persistence, and spread of resistant bacteria”.

“Antibiotics are valuable tools for reducing animal disease and suffering from bacterial infections, but decisions about which antibiotics to use in food animals and how to use them must be made with consideration of their potential impact on human health,” the CDC states on its website.

The CDC notes that people get infections from antibiotic resistant bacteria by handling or eating raw or undercooked food.

Antibiotic resistant bacteria can also be contracted from animal feces, either directly or when the stool gets into drinking and swimming water.

According to the CDC, resistant infections cause severe illness, and in some cases, death.

Most of the chicken eaten in Canada is produced by Canadian farmers. The country imports a small volume, mainly from the U.S.