Why Are Pig Farmers Still Using Growth-Promoting Drugs?

It’s one of the most controversial practices in agriculture: Feeding small amounts of antibiotics to animals in order to make them grow faster.

But what if the drugs don’t even work very well?

There’s some good evidence that they don’t, at least in pigs. They used to deliver a boost in growth, but that effect has disappeared in recent years, or declined greatly.

The reason for this is interesting, and even paradoxical.

Researchers think the antibiotics used to work by suppressing low-grade infections. In recent years, however, pork producers found other ways to accomplish the same thing through improved hygiene. This has occurred even while swine operations grow in size. As a result, the drugs have become largely superfluous — yet many farmers still use them.


Sixty years ago, when antibiotics were new, “people started treating animals, and feeding [the antibiotics], and finding that they had increased growth rates and feed efficiencies,” says Dritz. Nursery-age pigs, for instance, grew 12 to 15 percent faster with antibiotics. The animals also needed less feed to reach full weight. Other studies showed similar results in chickens and cattle.


Fast-forward to the 1990s. Dritz was starting his career as a scientist at Kansas State University, and pork production was changing dramatically. “We instituted this thing called multi-site production,” says Dritz.

Previously, pigs were born and raised in one barn, or in several barns close together. This meant infections could easily pass from one generation to the next, the way that kids share germs between their friends on the playground and their parents at home.




The groups are kept strictly separated from each other. If workers move between the groups, they’ll first have to change their boots.

When farmers adopted multi-site production, it cut down on disease — and pigs actually grew faster.


Dritz carried out some studies on pigs in these multi-site systems, comparing animals that received antibiotics with others that didn’t. “Lo and behold, in these studies, there wasn’t nearly the magnitude of the growth response,” he says.

In the “finishing” stage, the effect of antibiotics disappeared. Younger pigs grew a little bit faster with antibiotics, but the effect was smaller than had been observed earlier.




Once upon a time, this would have been left for farmers and their vets to hash out, but the use of antibiotics on the farm now is the focus of intense controversy. Critics of the meat industry say using these drugs to promote growth is irresponsible, because it increases the chances that bacteria will develop resistance to antibiotics, and some of these bacteria can infect humans.


Among farmers, there’s some grumbling about this. But at least for pork producers, dropping the drugs may actually save them money.
