Why should you spay or neuter your pets? Spaying and neutering helps prevent more pets from being added to the already large population of animals in shelters looking for homes. When your pet is in intact (not spayed or neutered), they will be driven to reproduce. Females will come in to heat, and both sexes may exhibit behaviours related to breeding such as territorialism, roaming, aggression, and urine marking. Spaying and neutering improves these behavioural issues. There are also health benefits: spaying and neutering greatly reduces or eliminates the risk of breast cancer, uterine and ovarian cancer and infection, prostate enlargement, and testicular cancer.