Ovariohysterectomy is the medical term used for the surgery so that female pets can no longer have puppies. It is commonly known as spay surgery. While the primary benefit is that the females no longer have an estrus or heat cycle, there are other reasons for this surgery. Spaying your pet before her first heat cycle virtually eliminates the chance of cancerous mammary tumors. It also prevents your pet from developing a pyometra. Pyometra is a severe and sometimes deadly infection in your pet’s uterus (for which the best treatment is an emergency spay, antibiotics, and a hospital stay on IV fluids).
Castration is the medical term for the surgery to neuter male pets so they can no longer sire litters. There are good reasons for this surgery other than sterilizing your pet. The chances for future prostate infections and prostate cancer are dramatically decreased when this surgery is performed on a young animal. Unwanted behaviors like urine marking, running (usually in desperate search for a female!), humping, and aggressive territorial actions can be avoided.