New puppy visits have to be one of my favorite appointments in veterinary medicine. Adorable puppies, excited owners, so many opportunities to lay the groundwork for a long and happy life together. We cover lots of topics: vaccinations, deworming schedules, training, nutrition. During the first visit, one of the most common questions I get with puppies is, “When should my pet be spayed or neutered?”
For a very long time, veterinary medicine offered a fairly standard response: Six months. But why is that? Is it truly in every pet’s best interests to be desexed, and if so, why this particular age? Let’s unpack this very important topic so that you understand the factors we consider when we give you our recommendation for spays and neuters.
Understand Exactly What a Spay or Neuter Entails
A spay, known in veterinary parlance as ovariohysterectomy, is the surgical removal of both the ovaries and the uterus in female dogs. While ovariectomies (removal of the ovaries, leaving the uterus) are becoming more common in other parts of the world, the complete ovariohysterectomy is still the main procedure taught and performed in the United States. In the dog, the ovaries are up near the kidneys, and the y-shaped uterus extends from both ovaries down to the cervix. An ovariohysterectomy is a major abdominal surgery that carries with it, like all surgeries, risk and benefit.
A neuter procedure, or castration, removes the testicles from a male dog. Unless the dog has a retained testicle (a condition known as cryptorchidism), a neuter procedure does not enter the abdominal cavity. While still a major surgery, it is not as complex as a spay in a healthy, normal male dog.
The Size of the Pet Matters
A main reason veterinarians recommend a spay at six months as opposed to six weeks is concern for anesthesia. Very small pets can be more of a challenge in terms of temperature regulation and anesthetic safety, though with today’s advanced protocols, we can very safely and successfully anesthetize even tiny pediatric patients. In a shelter environment, where highly trained and experienced staff perform thousands of pediatric spays and neuters a year, it is not uncommon to perform these procedures in pets closer to two-three months of age.
On the other hand, very large dogs are also more complicated to spay. Not only is the abdominal cavity larger and deeper, the blood supply is more robust and the fat in the abdominal cavity more difficult to maneuver around. Make no mistake, I would much rather spay a six-month-old dog of any breed than a five-year-old, 100-pound Rottie. As the difficulty increases, so does the risk of complication. With male dogs, the procedure does carry increased risk of complication as the pet grows but not to the same extent as a spay. Regardless, veterinarians perform so many of these procedures that we consider them fairly routine, even in large dogs, and the overall complication rate is still very low. Unless a pet has another underlying health issue, size should not be a reason to avoid the procedure.
Removing Hormones can be of Benefit
Another reason veterinarians settle on the six-month recommendation is that if a pet is not going to be bred, spaying a female dog before her first heat cycle has significant benefit in terms of reducing the risk of mammary cancer. While pets spayed before their first heat cycle have a 0.5 percent incidence of mammary cancer, that number torpedoes to 26 percent for pets spayed after their second heat cycle, with an overall incidence seven times higher for intact females than for spayed ones. Pyometra, a life-threatening infection of the uterus, is also very common in intact female dogs, and up to a quarter of intact dogs will develop it by ten years of age, according to one study. And obviously, a pet with no ovaries, testicles, or uterus cannot develop cancers or infections of those organs.
Testosterone has a great many effects on the dog that are decreased or eliminated when he is neutered. Behaviorally, neutered dogs are less aggressive, less likely to roam and be injured or hit by cars in their never-ending search for a mate and exhibit less of that frustrating humping behavior. Some boarding and daycare facilities do not accept intact pets, which can be a significant obstacle if you usually partake of these services.
Removing Hormones can be of Risk
Recent studies have linked early spay and neuter to a bevy of health risks: increased incidence of cranial cruciate ligament disease, osteosarcoma, hemangiosarcoma, or lymphomas in dogs that were spayed or neutered before sexual maturity. While these studies have received a great deal of attention, it’s also important to note that they are retrospective- they are looking back on medical records after the fact, which means the data is much more subjective and not necessarily definitive. While it isn’t unreasonable to make note of these associations and continue to study them, the scientific community is far from consensus on whether or not early spay and neuter causes these health problems, or is simply associated with them without being the cause.
There are two medical conditions that are generally accepted as being associated with spay: urinary incontinence and obesity. No one is sure why obesity is seen more in spayed females, as no studies have shown a change in metabolism after the procedure. Both conditions are treatable: incontinence with medications and obesity with diet and exercise.
Pet Overpopulation is Still a Significant Problem
Approximately four million dogs enter the shelters in the United States each year and of those, half are euthanized. Many of these are stray animals or unwanted “oops” pets abandoned by their owners. If you are not planning on breeding your dog as part of a well-researched and knowledgeable breeding program, he or she should be fixed. Dogs can begin their first heat cycle as young as six months, and you would be amazed at how easy it is for a motivated male to find her. Fences are destroyed, rock-hard soil tunneled through, six-foot walls scaled. Owning an intact female means making a commitment every seven months or so to keeping her under lock and key for the two-week duration of her heat cycle.
Are There Pets Who Should not be Fixed?
I fully support the role responsible breeders play in the canine world. Purpose-bred dogs play significant roles as assistance animals, in law enforcement and as beloved companions. I don’t believe in mandatory spay and neuter myself; as a pet owner I believe it’s up to you to understand the risks and benefits of all health decisions and choose what is best for your pet. For those who understand the risk of pyometra and reproductive cancers as well as the responsibilities of keeping an intact female from being accidentally bred, there’s certainly a good argument to make for waiting to spay. Many of those owners do still elect to spay their females once they are done having litters, which is an excellent compromise.
That being said, for the vast majority of companion animal owners, I still recommend spaying a dog before her first heat cycle as I believe that is the optimal balance of risk versus benefit. While the jury is still out on the benefits of waiting to spay until a pet is older, the known benefits of an easier surgery and recovery, living with a dog who does not go through the hassles of heat, avoiding unwanted pregnancy and eliminating the very real and ugly problem of pyometra and reproductive cancers makes this the ideal decision in my book.
For owners of male dogs, there is a little more leeway in terms of timing. Some veterinarians and breeders recommend waiting until a dog reaches their full size before neutering because of the possibility of increased joint disease and cancers in dogs neutered early, especially for large breed dogs. Unlike in females, where there is a known benefit for performing a spay before the first estrus, the benefit to neutering a dog at two is the same as it is at six months; the main deciding factors in these cases is whether the owner is willing to put up with the behavior of an intact dog for that long.
At the end of the day, this and all medical decisions surrounding your pet are your decision. Our job as veterinarians is to lay out the risks and benefits for your specific pet, and help you come up with a plan that is right for you.