The use of antibiotics in farm animals started out as a way of curbing disease among livestock, and of making animals grow bigger faster. It started out as a way of making the business more economical.
But it seems that the use of antibiotics in farm animals may have a higher cost in other areas. Overexposure to antibiotics through the food supply leaves us vulnerable to more antibiotic-resistant infections.
The Associated Press asserts that drug-resistant bacteria is regularly being found in meat sold in the U.S. "The report cites the widespread agricultural use, starting in the early 1990s, of a family of antibiotics that includes Cipro. Several years later, Cipro stopped working 80% of the time on deadly human infections it previously had cured."
The World Health Organization has cautioned for a number of years that this antibiotic use in farm animals is linked to drug-resistant bacteria affecting human beings. The European Union has banned the use of antibiotics in farm animals, unless it is to treat illness.
http://articles.latimes.com/2010/mar/13/opinion/la-ed-antibiotics13-2010mar13