Photograph by Volkmar K. Wentzel, Nat Geo Image Collection
Read Caption
It may be time to give the practice of feeding micro-amounts of antibiotics to animals to make them build muscle mass faster another look.
Photograph by Volkmar K. Wentzel, Nat Geo Image Collection
The Plate

Growth Promoters for Farm Animals: What If They Just Don’t Work?

The practice of giving food animals small doses of antibiotics has been around since at least the 1940s. In the earliest days they were used, these so-called growth promoters conferred huge benefits, sometimes doubling the weight of animals without requiring more feed.

But what if they no longer work? That’s the provocative question raised in a report by the Review on Antimicrobial Resistance, a British project that has been examining the best way to control antibiotic use on farms—and the antibiotic resistance that results—for more than a year.

The main thrust of the Review report released Monday in London is a proposal to set internationally agreed-to limits on how much on-farm antibiotics any country can use. This runs counter to control policies created by Europe and the United States, which addresses antibiotics categorically. For example, Europe banned growth promoters in 2006. The U.S. enacted voluntary controls on them at the end of 2013.

The Review says that setting curbs on quantities, instead of categories, will allow countries to find their own solutions to farm antibiotic use, whether they are industrialized nations already using lots of the drugs or developing ones just beginning to. It also argues that making amounts the target, instead of methods, will keep cheaters from simply relabeling one category as a different one—for instance, saying that what was a growth promoter is now a prophylactic antibiotic meant to prevent disease.

This could be a controversial approach, as growth promoter use has been the central tenet of campaigns against antibiotic overuse on farms. If they can be shown to no longer work, persuading farmers to abandon them—along with the significant antibiotic overuse they represent—might be easier.

View Images
A new report suggests setting limits on amounts, not types, of antibiotics for food animals. For more, see our related post in the Phenomena blog. Photograph by Balint Porneczi, Bloomberg, Getty

Today, about 32 million pounds of antibiotics are given yearly to U.S. livestock, as captured in this report to the FDA by drug manufacturers—and though the FDA doesn’t require them to say how their drugs are being used, more than 90 percent are given in a manner that indicates they might be growth promoters.

But, according to the British report:

There is growing evidence to suggest that antibiotics used as growth promoters do not have as much economic benefit as previously thought, particularly in countries with advanced farming techniques. This undermines the economic arguments in favour of using antibiotics for growth promotion: that the farmer will suffer productivity losses if he or she does not use growth promoters. Recently published papers suggest that the benefit from a growth perspective of using antibiotics sub-therapeutically in animals has declined over time… Studies in the U.S., Denmark and Sweden, after the 2000s, showed that growth promoters had less effect than they had done in earlier decades on the growth rate, and feed efficiency of animals. The impact after the 2000s was typically less than 5 percent.

The Review on Antimicrobial Resistance sums up what some scientists have been saying quietly for a while.

As far back as 2007, researchers at Johns Hopkins University’s Bloomberg School of Public Health calculated that growth promoters conferred so little benefit that, even though the drugs are generic and therefore cheap, farmers lost about one cent on every chicken fed them. Earlier this year, researchers from the Center for Disease Dynamics, Economics and Policy, and from Princeton University, estimated that growth promoters globally make a difference of no more than 1 to 3 percent in how much weight animals gain.

And in a little-noticed report released immediately before Thanksgiving, federal scientists said that withdrawing growth promoters from meat production in the United States could make a difference of as little as 1 percent in yields and prices.

There’s an important caveat, though, to all these findings, and that is that growth promoters make the least difference where farms are already modern, high-tech and clean. That means they might still be effective in developing nations, where farming practices are less advanced, and where meat consumption is growing the most quickly.

And that means the battle over farm antibiotic use could, like climate change, become a dispute that pits rich industrialized nations against emerging economies that have the same appetite for meat that the West does—and intend to take the same hazardous path to achieve it.

For more about that dispute, and how the new proposal for controlling farm antibiotic use reflects global alarm over antibiotic resistance, see the companion post at our sister blog, Phenomena.