companions are surgically prevented from reproducing. In males the operation is called ‘castration’; in females, ‘spaying’. Both of these operations are performed under general anaesthetic.
When a male is castrated both testicles are removed, which takes away the main source of the male hormone testosterone. As the testosterone levels fall to a minimal level after castration, the effects of this hormone are also reduced.
When a female is spayed both the ovaries and the uterus (womb) are removed. This means that the animal is unable to become pregnant, and will no longer come into season.