An estimated 70 % of all the antibiotics produced in the United States are not used to treat humans, but animals-and not because they're sick.  These antibiotics are added to animal feed to promote growth or prevent illness for animals in confinement housing. Questions about how these practices are in turn affecting human health have prompted action in Congress.

Legislation in House, called the "Preservation of Antibiotics for Medical Treatment Act" would restrict seven classes of antibiotics important to human health from being used in animals-except for medical reasons. 

Dr. Margaret Mellon is a senior scientist and director of the Food & Environment Program at the Union of Concerned Scientists.  She serves on the U.S. Department of Agriculture's Advisory Committee on Biotechnology and 21st Century Agriculture and she teaches a course in biotechnology and the law at Vermont Law School.  She spoke with VPR's Jane Lindholm about the issue.