Any surgical procedure intended to end fertility permanently (see contraception). Such operations remove or interrupt the anatomical pathways through which the cells involved in fertilization travel (see reproductive system). They are relatively simple and more than 99percnt effective. The operations used in humans are vasectomy in men and tubal ligation (tying off and blocking or cutting of the fallopian tubes) in women. Though these operations are considered permanent, the development of microsurgery has improved the chances of reversal. Animals are sterilized by castration in males and spaying (removal of the ovaries) in females.

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