I started veterinary school in 1996. Three years earlier, the American Veterinary Medical Association had resolved to support the concept of early spays and neuters in dogs and cats. (Back then the AVMA carried a great deal of sway — it would be another decade before it would destroy its reputation with self-aggrandizement, disregard for animal welfare, and contempt for its members.) The concept of shelter medicine was beginning to mature, and veterinarians as a whole were greatly concerned about pet overpopulation (and the consequent euthanasia of millions of healthy, adoptable animals).
By the time I graduated in 2000, it was an article of faith: Dogs and cats should be spayed and neutered as early as reasonably possible. The message was clear. If you could get your hands on a puppy and a scalpel, start snipping.
I strongly urge you to be leery of any medical professional who subscribes to articles of faith. Good doctors don’t take things on faith. They want proof.
Around the time I graduated, various studies were published that, in the minds of many vets, offered the necessary proof. One that stands out in my memory is titled, “Long-term outcome of gonadectomy performed at an early age or traditional age in cats.” The study compared the outcomes over three years of a large number of cats who were spayed either before or after six months of age, and concluded that spaying or neutering earlier carried essentially no increased risk relative to spaying or neutering later.
The study, as the authors admitted, was not without limitations. All studies have limitations. And in the context of the current discussion here on Dogster, the study has one glaring limitation: It was a cat study.
From a population standpoint, there is no doubt that spaying (I’m not so sure about neutering — see below) is in the best interest of dogs. It is not possible to deny that millions of unwanted dogs are needlessly euthanized due to overpopulation.
Where I live, there also is a social stigma against owners of intact animals. A male owner of an intact male dog may be presumed to be making up for his own shortcomings in the manhood department. Owners of unspayed female dogs are often presumed to be too lazy, irresponsible, or stupid to get around to spaying their dogs.
In my experience, the majority of owners of intact dogs fall into the second category. Their dogs are intact due to owner negligence and nothing more.
But there is a minority who are the exact opposite. They are among the most responsible and informed dog owners one might ever meet. They have chosen not to spay or neuter their dogs because they have studied the risks and benefits — not for populations of dogs, but for their individual dogs — and have concluded that spaying or neutering was not in their dogs’ best interests. These people have braved the social stigmas and often weathered grief from veterinarians. They also have managed to keep their dogs from reproducing. How and why did they reach their decisions?
It turns out, there are both benefits and risks to spaying and neutering. And the topic of when and even whether to spay or neuter is becoming increasingly controversial in veterinary medicine. I imagine that the topic is going to be drawing much more attention in the future as more heretics question the faith of the profession. It will pit shelter vets, humane advocates, and some veterinary oncologists against orthopedic surgeons, endocrinologists, and other oncologists. Spaying and neutering is a political topic, and the argument has the potential to get nasty. (In fact, I have seen otherwise civil experts turn hostile when discussing the subject.)
Let’s run through some of the benefits first. The risks will come next.
The most cited benefit of spaying and neutering is population control. I’m going to come out and say that I don’t feel this benefit applies to male dogs. Under most circumstances, females alone control the rate of reproduction in dogs. Imagine a population of 1,000 male dogs and 1,000 female dogs. If one were to neuter 990 of the males and leave everyone else intact, the end result would be 10 happy but exhausted intact male dogs, 990 oblivious neutered male dogs, and 1,000 pregnant female dogs. The only way for neutering to significantly impact overpopulation is to neuter every male in a population, and that’s rarely going to happen.
Every unspayed female, however, has the potential to increase overpopulation. And spaying also has the potential to benefit individual females by reducing unplanned or “accidental” pregnancies and the myriad health risks they present.
How do those “accidental” pregnancies occur? It turns out that intact animals may behave differently, on average, from those who have been neutered and spayed. For most dog owners, the behavior of altered animals is more desirable. Neutered males are less likely to engage in aggression, urine marking, and leg humping. Both genders are less likely to escape from the house in order to seek trysts. Of course, sometimes they don’t need to escape. I have met plenty of people who were surprised that their two intact dogs mated.
Those trysts carry risks other than pregnancy. Transmissible venereal tumor is a common sexually transmitted disease in developing countries where spaying and neutering are uncommon. Coitus itself can cause injury if the dogs pull apart too aggressively while they are “tied.” They also are vulnerable to aggression while in this position.
Mammary (breast) cancer is markedly less common in dogs who are spayed before their first heat. Uterine, ovarian, and testicular cancer are essentially unheard of in altered animals. Prostatitis appears to be less common in neutered males.
Finally, a life threatening infection of the uterus called pyometra is not uncommon in unspayed females. It is extremely rare in females whose ovaries have been removed.
What are the downsides to spaying and neutering? Let’s start with the procedures themselves. Surgery is painful, and a surprising number of veterinarians use inadequate pain management practices.
Spaying and neutering predispose dogs to weight gain and obesity, which in turn can lead to a host of other problems, ranging from breathing difficulties to skin infections to arthritis and beyond.
Altering a dog before maturity appears to significantly increase the risk of a major and common orthopedic problem called cruciate ligament rupture. I have met a few orthopedic surgeons who were passionately against spaying and neutering, especially before a dog is fully grown.
The benefits of spaying and neutering are not an open-and-shut case in the world of oncology. Neutering is a significant risk factor for the development of canine prostate cancer. A terrible bone cancer called osteosarcoma appears to be significantly more common in altered individuals. Osteosarcoma, in my experience, is a greater threat than mammary tumors, uterine cancer, ovarian cancer, and testicular cancer combined.
Finally, there are some who suspect that spaying and neutering may contribute to decreased longevity overall in dogs. These suspicions gained prominence after a study was published that showed a link in Rottweilers between extreme longevity and intact status.
Ultimately, what is needed is a large cohort study comparing lifelong outcomes in dogs who are altered early in life, later in life, or not at all, with confounding variables ruled out. Such a study would be difficult and expensive in a world where three years is considered “long term,” but it would have the potential to turn the veterinary world upside down (or not).
Meanwhile, for someone trying to make a responsible decision about when and whether to spay or neuter his dog, many factors ultimately should come into play. Some of the factors might include breed, ancestral proclivity towards cancer, local laws that mandate spaying or neutering, tolerance for potentially unpleasant behavior, expected activity levels, and ability to prevent unwanted pregnancies.
On average, I believe that most dogs experience significant health benefits from being spayed or neutered. And on average, I believe that the best time to perform the procedure is just before puberty in females — when they are as close to fully grown as possible, but before the risk of mammary tumors (and pregnancy) increases. However, your dog may not be average. And I reserve the right to change my opinion as more evidence develops. I practice medicine, not ideology.
Also, the benefits of neutering male dogs before puberty aren’t clear cut. This is especially true for larger dogs who are at increased risk of cruciate ligament injury: It might be best to let them go through puberty before they are neutered. However, be aware that some individuals (they are rare in my experience) undergo behavior changes during puberty — including severe aggression — that do not reverse when they are neutered.
I strongly recommend that you seek a good veterinarian’s advice on the matter. Here is how you can tell whether a veterinarian is good: She will acknowledge that the matter of spaying and neutering is complicated. You can expect such a vet to engage in a meaningful, heartfelt conversation — but she may not be able to offer a clear answer.
For now, there is no clear answer.