The only United States Food and Drug Administration-approved growth hormones for food, particularly for beef cattle and sheep, are natural and synthetic versions of the animal's naturally-occurring hormones. These hormones include the animal's natural testosterone, estrogen and progesterone, and the hormones' synthetic equivalent, such as trenbolone acetate or zeranol. The use of hormones in beef cattle and sheep has been in practice and has been approved by the FDA since the 1950s.
Using growth hormones on beef cattle and sheep increases the animals' growth rate by 20 percent and increases their efficiency of converting the feed that they consume into meat. Prior to approving any of the drugs, the FDA requires sufficient information and studies that show that the hormones do not harm the animals being treated, or the environment. Some of these hormones remain in the meat after the cattle or sheep have been slaughtered. The FDA has guidelines regarding the acceptable safety limits of hormone content in meat.
These hormones, also referred to as steroid hormones, are usually administered to the animals in the form of pellets. These pellets are implanted on the skin behind the animals' ears, and gradually dissolve and are absorbed. The ears with the growth pellets are discarded when the animal is slaughtered. Although some growth hormones remain in the meat, they pose no risk to those who consume them, according to the FDA. Growth hormones are not approved for use in dairy cattle, pork, veal calves or poultry.