Traditionally rats are not generally neutered. However it has recently been shown that if female rats are neutered at a young age the incidence of mammary tumours and of pituitary tumours is greatly reduced. This is because most of these tumours are hormonally stimulated. Neutering older female rats after several reproductive cycles will not affect the development of these tumours but will prevent disease or cancer of the reproductive tract as this is removed in the neutering surgery.
Male rats are usually neutered to reduce aggression. They are usually calmer and easier to handle after neutering. These behavioural changes are more marked when the neutering occurs at a young age. Neutering males will also prevent testicular cancer although this is rare.
Male and female rats can be neutered from four months of age.
Mice are rarely neutered prophylactically. Males are sometimes neutered to prevent intermale aggression and/or to prevent unwanted pregnancies. Females are neutered as a treatment for disease of the reproductive tract that will not respond to medical treatment.