One of the most striking patterns in modern American agriculture is the increasing use of antibiotics as a regular supplement in the feed and water consumed by cows, pigs and especially poultry. http://www.nytimes.com/2001/01/09/opinion/09TUE2.html or, if paranoid, try http://partners.nytimes.com/2001/01/09/opinion/09TUE2.html
