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, Lowa, 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.

　　1．One of the advantages of using antibiotics in the past is that it ________.

　　A．helped animals grow faster

　　B．decreased the death rate of animals

　　C．helped animals have a better appetite

　　D．increased animal reproduction

　　2．Pigs were more easily infected in the past because ________.

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