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  . As a result, the drugs have become largely superfluous -- yet many farmers still use them. To understand how this happened, you have to step back in time, says Steve Dritz, a specialist in pig nutrition at Kansas State University. 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," he says. 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. In the 1980s, a new set of studies found similar effects. So the growth-promoting effects of antibiotics became standard practice among meat producers. Fast forward to the 1990s. Dritz was starting his career as a scientist at Kansas State University, and pork production was changing dramatically.  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. Under the new system, when piglets are weaned, they move to a whole different place. That new site is carefully scrubbed and free of disease. Craig Rowles, who runs a large swine operation in Carroll, Iowa, shows me one such room. There's not a piglet in sight. "This room just got completely washed and disinfected, and now it's going to sit here and dry for a while," he says. A whole group of pigs will come in here together, and later they will move out together to yet another site. "That group of pigs will stay together until they go to market," Rowles says. The groups are kept strictly separated from each other. If workers move between the groups, they first have to change their boots. When farmers adopted multisite production, it cut down on disease -- and pigs actually grew faster. Pigs were more easily infected in the past because   _  .
they used antibiotics they were always close together they were raised on the playground they moved from one farm to another
Question: 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  . As a result, the drugs have become largely superfluous -- yet many farmers still use them. To understand how this happened, you have to step back in time, says Steve Dritz, a specialist in pig nutrition at Kansas State University. 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," he says. 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. In the 1980s, a new set of studies found similar effects. So the growth-promoting effects of antibiotics became standard practice among meat producers. Fast forward to the 1990s. Dritz was starting his career as a scientist at Kansas State University, and pork production was changing dramatically.  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. Under the new system, when piglets are weaned, they move to a whole different place. That new site is carefully scrubbed and free of disease. Craig Rowles, who runs a large swine operation in Carroll, Iowa, shows me one such room. There's not a piglet in sight. "This room just got completely washed and disinfected, and now it's going to sit here and dry for a while," he says. A whole group of pigs will come in here together, and later they will move out together to yet another site. "That group of pigs will stay together until they go to market," Rowles says. The groups are kept strictly separated from each other. If workers move between the groups, they first have to change their boots. When farmers adopted multisite production, it cut down on disease -- and pigs actually grew faster. Pigs were more easily infected in the past because   _  .
A. they used antibiotics
B. they were always close together
C. they were raised on the playground
D. they moved from one farm to another
Answer: