Currently, six different steroidal hormones are approved by the FDA for use in “food animals.” These are the natural hormones estradiol, progesterone, testosterone, and the synthetic hormones trenbolone acetate, progestin melengestrol acetate, and zeranol, all of which make animals grow faster and/or produce leaner meat for food. Dairy cattle are often treated with recombinant bovine growth hormone (rBGH) to increase milk production. Hormones are banned for use in poultry in the . (but that doesn’t stop chicken producers from marketing their birds as hormone-free!).