Estrogen: steroid hormone involved in the development of the secondary sex characteristics of women, in the regulation of the menstrual cycle and ovulation and pregnancy. Androgen: term that encompasses the male sex hormones, which are g that induce and maintain secondary sexual characteristics in males. The main androgens are testosterone and androsterone. Progesterone: hormone produced by the cells of the corpus luteum of the ovary. The corpus luteum is a structure that develops in the ovary, in the place that occupied a mature egg that has been released during ovulation. Therefore, the progesterone level rises during the second half of the menstrual cycle. Anabolic agents can be administered via oral or parentalmente. They are given orally to the pigs as food additives and this is the way to choose if you have intensive fish farming. Anabolics are administered as implant subcutaneous in cattle, sheep and poultry, or injected as oily solutions in horses and some calves The anabolic used in oily to be used intravenous solutions have the disadvantage that its action is short are generally administered to pets for therapeutic reasons. It is more widespread for purposes of production in beef cattle animal subcutaneous implants at the base of the ear, and they should be subject to a period of retraction or with specific doses. The implant is put at the base of the ear, because the hormones that are given are artificial and the body takes longer to integrate them, prevents put them in places that are for human consumption. Once the implant, the concentration of the hormone supplemented rises quickly and waste will be greater during the initial period after implantation. For this reason, when the hormones are synthetic, there is a time that must elapse enters the date of the implant and the date of the slaughter. The time varies depending on the used anabolic, and the legislation of each country. In the case of natural hormones it is not necessary that period expires.