Most pet dogs are spayed (females) or neutered (for males) to remove reproductive organs and prevent pregnancy. But health issues provide other compelling reasons for Spaying and Neutering dogs.
Female dogs have a high incidence of cancers of the reproductive system. Spaying removes the ovaries and the uterus, preventing the production of estrogen, which leads to most of the reproductive cancers. A vast majority of unspayed older females contract a life-threatening infection of the uterus, call pyometra. This infection is caused by problems with progesterone, another female hormone which is eliminated through spaying. Female dogs should be spayed before their first heat, if possible, which generally occurs between six months and one year of age.
Males that are not neutered often exhibit extremely aggressive behaviors, which can be dangerous to them, other animals and people. A dog that was well-behaved and calm in its youth can suddenly show a pack mentality and become more aggressive, chase cars, try to get loose to roam freely, or bark and growl a lot all as a result of high testosterone levels. Many of these habits become hard to break. A male dog neutered between six months and one year of age will retain its youthful calm.
Spaying and Neutering are common surgeries. They require some form of anesthesia and most vets prefer for the dog to remain in the hospital overnight. Your dog may be under the weather for a few more days as a result of the surgery, but will heal within a matter of a week or so.