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  • Research shows that spay-neuter can increase the risk of joint disorders and certain cancers.
  • The likelihood of negative health outcomes varies widely between breeds and sexes.
  • Decisions about whether to spay-neuter should be reached through informed discussion with a veterinarian.

Bans at doggie daycare, disapproval at the dog park: the United States public is not fond of dogs that still have their reproductive organs. Spay-neuter — the veterinary surgical practice of removing a dog’s ovaries or testes — is the norm for most U.S. dogs. It’s estimated that 80 percent of U.S. dogs are spayed (in the case of females) or neutered (males), and leaving your dog intact might get you branded an irresponsible dog owner. In fact, many states require all dogs that pass through shelters be spayed or neutered before they’re rescued, often at just a few months old.

Yet a growing body of research suggests that spaying and neutering dogs, especially young dogs, can increase their chances of developing some serious conditions.

Reasons to Consider All Options Before Spaying or Neutering a Puppy

Dr. Benjamin Hart of the University of California, Davis, has been researching the effects of spay-neuter for a decade, with support from the American Kennel Club Canine Health Foundation. His first paper on the subject, published in 2013, revealed that Golden Retrievers that had been spayed or neutered had a correlation of being three or four times more likely to develop certain cancers, including lymphosarcoma and hemangiosarcoma, and also more likely to develop joint problems such as hip dysplasia and damage to the cranial cruciate ligament. The team later published data on German Shepherd Dogs and Labrador Retrievers, finding that early spaying and neutering had varying effects on these dogs’ likelihood to develop joint disorders, cancers, and urinary incontinence.

Now, Dr. Hart and his team have completed a further round of retrospective research, investigating tens of thousands of dogs from 35 breeds, and focusing on early spay-neuter, carried out before the dog reaches sexual maturity. They found that the procedure’s health consequences vary widely between breeds. “It’s hard to predict which ones will and which ones do not have an increase in cancers or joint disorders with early spay-neuter,” Dr. Hart told me. For instance, the researchers found that in almost all dogs weighing less than 20 kilos (about 45 pounds), there was no increased incidence of the studied joint problems and cancers compared to intact dogs. All, that is, except for the Shih Tzu. Early neutering of male Shih Tzus, the team discovered, was associated with higher rates of some of the cancers studied.

And when it comes to dogs weighing more than 20 kilos, the study found that the impact of early spay-neuter varies hugely across breeds and sexes. For instance, since most small dogs didn’t experience higher rates of the studied cancers and joint problems, Dr. Hart conjectured that at the other end of the scale, Great Danes might suffer them at a high rate. Yet he found that the gentle giants had no increase in joint disorders after early spay-neuter. “That was completely unexpected,” Dr. Hart told me.

And the variability doesn’t end with breed and sex. Negative health outcomes from spay-neuter were often limited to dogs that were neutered early, i.e. before they reach sexual maturity. But this isn’t always the case. For instance, female Golden Retrievers spayed after 12 months of age were four times more likely to develop hemangiosarcoma as intact females and even early-spayed ones, according to Dr. Hart’s 2013 publication.

Doesn’t Spaying or Neutering a Dog Prevent Behavioral Problems and Certain Kinds of Cancer?

So how and why did spaying or neutering dogs at six months come to be the norm? “Population control” is the most common answer. Canine cognitive scientist Dr. Alexandra Horowitz, writing in the New York Times, describes the way spaying and neutering dogs rapidly became an easy answer to the apparent problem of stray dogs and overfull shelters. But as we’re learning, an easy answer isn’t always the best one.

For a long time, many also believed that spay-neuter could prevent behavioral problems as well as prostate and mammary cancers. But when Dr. Hart investigated these claims, he found a more complicated picture. For instance, his research revealed that neutering male dogs with aggression problems only resolved aggression in 25 to 30 percent of cases. In other words, three out of four dogs did not show an improvement in aggressive behavior after neutering alone. And significantly, those behavioral improvements were equally likely if neutering was delayed until after a dog had reached sexual maturity.

Neutering also does not prevent prostate cancer. “As a matter of fact,” Dr. Hart told me, based on available data, “prostate cancer in males is more common in neutered than intact dogs.”

Existing studies on the incidence of mammary cancer are less conclusive, but further research is ongoing through the AKC Canine Health Foundation and other institutions, so there’s more guidance on decision-making for the disease on its way. Meanwhile, Dr. Hart points out that both prostate and mammary cancer are relatively uncommon in dogs, whether they’re intact or neutered/spayed. And testicular cancer, though a more common occurrence in older intact male dogs, offers better treatment outcomes compared to other cancers.

So, Should You Spay-Neuter? What the Experts Advise Today

So what should dog owners do? Should you spay or neuter, and if so, when? “The take-home message is that it depends on a lot of different factors. We can’t just make a blanket recommendation for all dogs,” Dr. Sharon Albright, Manager of Communications and Veterinary Outreach at the AKC Canine Health Foundation, told me. “It depends on what breed the dog is; what the major health concerns are for that breed, or whatever breeds make up that mixed-breed dog; what the owner intends to do with the dog … and then obviously if it’s a male or a female.” Dr. Albright recommends speaking to your veterinarian to reach a decision that takes into account the recent research as well as the dog’s expected lifestyle. For instance, owners of active dogs (whether they’re jogging partners or dog sports champions) should be well aware of the risk of joint problems before making a decision on spay-neuter.

An adult Puli with cords running alongside a younger Puli

Dr. Hart agrees. “One of the things I emphasize is the need for a paradigm change with regard to veterinarian-client relationships,” he told me, adding that he and his team would like the question of whether and when to spay or neuter to be a true discussion point between the veterinarian and the client, in which both are equipped with all the necessary information about the likely impacts on the dog in question.

Dr. Albright also stresses that it’s important to take into account how serious, common, and treatable the possible health outcomes are on each side of the spay-neuter decision, while also considering the health and well-being impacts of unwanted pregnancies.

While you make that calculation, bear in mind a reminder from Dr. Hart: although the risk of developing certain cancers and joint disorders increased when certain breeds were spayed or neutered early, most dogs will not develop these conditions. The emerging research can give us a picture of the likelihood of certain outcomes, but can never fully predict what life will look like for your particular dog.

And that’s because each dog, like each human, is an individual, with his or her own set of health and lifestyle needs and quirks. For decades, America’s dogs have been treated with a blanket rule about their reproductive organs. Though more research on spay-neuter is needed, with the information already available, dog owners can start working with veterinarians to make better, more informed decisions about what’s best for these beloved family members.

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