Check out this NPR article
The article says it all. Here are some snippets from it:
"In 2010, the world used about 63,000 tons of antibiotics each year to raise cows, chickens and pigs, the study estimated. That's roughly twice as much as the antibiotics prescribed by doctors globally to fight infections in people."
""We project in the next 20 years, world consumption of antibiotics in animals will go up by two-thirds," he says. "The implications for the effectiveness of our antibiotics could be quite devastating."
""But the circumstantial evidence, linking use in animals to drug-resistant bacteria in humans, is exceedingly strong,"