"Certain hormones can make young animals gain weight faster. They help reduce the waiting time and the amount of feed eaten by an animal before slaughter in meat industries. In dairy cows, hormones can be used to increase milk production. Thus, hormones can increase the profitability of the meat and dairy industries.
here are six different kinds of steroid hormones that are currently approved by FDA for use in food production in the US: estradiol, progesterone, testosterone, zeranol, trenbolone acetate, and melengestrol acetate. Estradiol and progesterone are natural female sex hormones; testosterone is the natural male sex hormone; zeranol, trenbolone acetate and melengesterol acetate are synthetic growth promoters (hormone-like chemicals that can make animals grow faster). Currently, federal regulations allow these hormones to be used on growing cattle and sheep, but not on poultry (chickens, turkeys, ducks) or hogs (pigs). The above hormones are not as useful in increasing weight gain of poultry or hogs."