A growth hormone found in pigs; injections of or implants containing this hormone cause pigs over 100 pounds to gain more muscle and less fat. In past years, the hormone was very expensive because it could only be taken from the pituitary glands of slaughtered pigs, but in the early '90s researchers learned how to genetically engineered the bacterium E. coli to produce it. The FDA has not yet approved this hormone for use. See also bovine somatotrophin.