Hormones are proteins produced by organs of the body that trigger activity in other locations. Cows produce a natural hormone called bovine growth hormone, or BGH, that causes them to make milk. They have figured out how to clone the gene in order to produce BGH artificially. Some cells are removed from a cow, and the gene for BGH is cut out of their genome. The gene is then injected into bacteria.
Bacteria reproduce very quickly.
As each new cell of bacteria is made, a new copy of the gene also is made. In this way, millions of copies of the gene are produced in a short time. With millions of copies of the gene, lots of BGH gets produced. The BGH is then strained out of the bacteria and sold as a drug. Giving cows this drug increases the amount of milk they produce by as much as 15 percent.