Before I became involved with holistic medicine, I would have said that all pets should be spayed or neutered at six months of age before the females have their first heat cycle. This belief is still held by most traditional veterinarians.
The single biggest reason to spay or neuter is population control. Thousands of animals are euthanized at shelters every year due to unwanted production of puppies and kittens. However, if we could all be responsible pet owners and keep our young pets from being accidentally bred, our pets would be healthier by allowing them to reach full maturity before considering spaying or neutering.
I do not support pediatric spaying and neutering, but I do understand the usefulness when adoption agencies and shelters want to get puppies and kittens adopted and know they will not be able to breed. Some studies have shown long-term health consequences of early spay/neuter, including hypothyroidism, joint problems, urinary incontinence, and more frequent urinary tract infections. Other studies have shown long-term health benefits of leaving pets intact, including decreased risk of cancer.
On the other hand, mammary cancer dramatically increases in unspayed older females. Current studies show that spaying between twenty-four and thirty months of age will allow females to reach maturity and may have some beneficial protective effects against certain cancers, while still having a low incidence of mammary cancer.
The incidence of uterine infection (pyometra), which is life-threatening, also increases with age. Owners of intact females should understand symptoms of infection, which may include increased thirst and urination, decreased appetite, lethargy, and possibly vaginal discharge. Dogs and cats with discharge are easy to diagnose, while those that do not show discharge are more challenging. Pyometra generally occurs approximately six to eight weeks following a heat period.
Ovary-sparing spay, where the uterus is removed to prevent pyometra, while leaving the ovaries in place, is becoming more popular. Not many veterinarians will perform the procedure. Risk of mammary cancer remains with this type of spay. Whether a pet parent decides on ovary-sparing spay versus traditional spay is a personal decision that should be discussed with the veterinarian.