Removal of the testes (testis). The procedure stops most production of the hormone testosterone. If done before puberty, it prevents the development of functioning adult sex organs. Castration after sexual maturity makes the sex organs shrink and stop functioning, ending sperm formation and sexual interest and behaviour. Livestock and pets are castrated to keep them from reproducing (see sterilization) or to create a more docile animal. In humans, castration has been used for both cultural (see eunuch, castrato) and medical (e.g., for testicular cancer) reasons.