Sterilization is a surgical technique leaving a male or female unable to procreate. It is a method of birth control. For non-surgical causes of sterility, see infertility.
In animals, castration (removal of the testes) and salpingo-oophorectomy (removal of the ovaries and fallopian tubes), called "neutering" or "spaying" when applied to pets, are used to reduce or eliminate sexual behaviour, and to prevent conception, heat and possible uterine diseases in females, potentially prolonging an animal's lifespan. Due to the hormonal changes involved with both genders, this will definitely cause minor personality changes in the animal. When these changes are undesired, a different method of sterilization can be used, such as vasectomy in males or tubal ligation in females. A typical example of this practise is when male cats are subjected to vasectomy so that they are able to mate with females, thereby "bringing them off heat" (terminating estrus). This keeps the condition of the female from deteriorating due to the extra energy that is expended during estrus. A vasectomized male cat is called a "teaser tom" by cat breeders.
Animal control organizations urge owners who do not keep animals for the specific purpose of breeding from them to have their pets spayed or neutered in order to prevent an increase in the population of stray animals. These stray animals are often malnourished, and are frequently euthanized by animal welfare societies.