Chapter 3: What’s Happening to My Doggy?

Spaying and neutering are good for the whole. But what does it do to the individual animal?

This is the third installment in a series.

Moose and I have a routine. Just as day breaks, he gets up, comes to my side of the bed, sticks his head under the pillow where I’m safely ensconced, and pokes his nose in my face. I pretend to be asleep until he gives up and trots to my wife’s side of the bed, and she pretends to sleep until he comes back to me and tries again. We do this several times before the loser finally gets up to feed the dog. Then, we all go to a middle school up the street from our house that has become a de facto dog park during the pandemic. Moose runs around with the neighborhood mutts, and we engage in dog talk with their owners. 

It was on one of these trips to the middle school when we met Tiny, a chubby six-month-old golden retriever puppy whose name was certainly meant to be ironic. Tiny had a small patch of fur shaved off her leg, and her owner told us that she’d just been spayed. I opened my mouth, just about to speak, and then glanced over at my wife, who was giving me a look that said, “Don’t say it unless you want a divorce before lunch.” I shut my mouth; she changed the subject. 

Tiny’s owner had good reason to spay his puppy at six months: His vet probably told him too. For decades, early spaying and neutering have been standard practice, part of being a responsible dog owner. It’s just what you do, and while more and more vets advise waiting until at least a year, many today still recommend spaying or neutering under six months, and shelters and rescues often require it for adoption. But what I would have told Tiny’s owner had my wife not given me the look, is that there may be downsides to this practice, and they’re serious. 

In the last chapter of Moose Nuggets, we explored how—and why—dog desexing went from rare to expected in the span of a few decades. That chapter was about the big picture, about how spaying and neutering programs prevented millions of unnecessary deaths and how this might just be the biggest animal protection story in modern history. But despite the successes of this movement, there are costs, and in this chapter, we’re going to zoom in and find out what, exactly, this means for the dogs we can’t help but love—even when they wake us up.

If you visit the website for the American Society for the Prevention of Cruelty to Animals, one of the largest animal welfare groups in the world, there’s a clear message: Spaying and neutering is good for your pet. 

“Here are some of the medical benefits,” the site reads: “Your female pet will live a longer, healthier life. Spaying helps prevent uterine infections and breast tumors, which are malignant or cancerous in about 50 percent of dogs and 90 percent of cats. Spaying your pet before her first heat offers the best protection from these diseases. Neutering your male companion prevents testicular cancer and some prostate problems.”

But is this good advice?  

To find out, I called Ben and Lynette Hart, two of the foremost animal researchers in the U.S. Both longtime faculty at the School of Veterinary Medicine at the University of California, Davis, the Harts have published hundreds of papers on everything from elephant yawning to urine spraying in cats, but they have a particular interest in the health effects of spaying and neutering on dogs.  

In 2013, the Harts completed the first major study on joint disorders and cancer rates in dogs that have been spayed or neutered. For this study, they analyzed hospital records from the UC-Davis School of Veterinary Medicine, specifically those of golden retrievers. They found that rates of some cancers (e.g., cancer of blood vessel walls, lymphatic cancer, and mast cell tumors) increased in dogs that had been neutered, especially females. They also found that spayed/neutered dogs were more likely to have knee ligament damage and hip dysplasia, a disorder my childhood Lab suffered from that made walking so painful she sometimes dragged her back legs behind her when she walked. And, yes, we spayed her early. At the time, it was just what you did. 

Rates of these disorders varied by sex as well as the age at which the dog was spayed or neutered, but the Harts had clearly tapped into something important. Golden retrievers are one of the most popular dog breeds in America, and their findings showed that spaying and neutering might actually be causing them suffering. And so, you probably would think that the veterinary establishment might have been receptive to this information.

Initially, it wasn’t. The Harts had so much difficulty getting a major journal in their field to consider their paper, they ended up publishing at the open-access journal PLOS-One, where it’s available without charge to anyone. By now, their paper has been viewed nearly 400,000 times. But still, Ben told me, some vets didn’t want to hear it. 

“At first, there was a lot of pushback within the profession. They said, ‘We don't want you to talk about it. We don't want to disturb how we've been handling this.’”

“We joked about tomatoes being thrown at us,” Lynette broke in. 

The Harts did not stop talking about it. As of now, they’ve analyzed 35 pure breeds, as well as five categories of mixed breeds, and Ben told me that the ASPCA’s recommendation to spay or neuter every dog is, “in a nutshell, bad advice.” There’s just too much variation for there to be one hard and fast rule for all animals. 

While the effects of spaying and neutering vary across breed, age, and sex, as a general rule, the Harts found that the bigger the dog and the earlier the desexing, the greater the risk of debilitating joint disorders and some cancers. Most small breeds, however, are a different story. 

“Small breeds get some cancers and joint disorders but there's very few in which neutering plays a role,” Ben said. 

Moose, however, isn’t small, and he’s also part golden retriever, a breed that does have high rates of cancer in general. And because he’s the dog I care most about, and the dog whose testicles I’m considering cutting off, after I talked to the Harts, I added another tick to the Keep Moose’s Balls list I’d been keeping. Cancer? In my boy? I pictured Moose in a chemo ward, confused, in pain, and bald as Jean-Luc Picard. I really didn’t want to shave my entire body in solidarity. “No way,” I thought to myself. “He’s keeping them.”

But what about behavior? Conventional wisdom tells us that spaying and neutering makes dogs easier, more trainable, less of a headache. And in some ways, this makes intuitive sense.

Spaying, which involves removing the dog’s ovaries, fallopian tubes, and uterus, prevents female dogs from going into heat, which, if nothing else, is definitely more pleasant for the owner. The estrus cycle, as it’s known, can involve bleeding from the vulva, and while no one has made doggie tampons yet, they do make a sort of period panties for pups. (Growing up with only spayed dogs, I had no idea that this happened until my 20s, when a friend’s terrier bled on my carpet. I can see why people want to prevent this.) 

Males dogs aren’t exempt from the changes either. They can reportedly smell a bitch in heat from far away, and intact male dogs are more likely to stray in the attempt to find a fertile partner. This, of course, puts them at risk of getting lost or hit by a car.

Neutering, which involves removing the testes, dampens the sex drive by eliminating the dog’s main source of testosterone. But this, like estrogen in females, is an important hormone for development, and it’s one of the reasons neutered dogs are more likely to have joint disorders. Still, as we know from the effects of testosterone on humans, it can also make dogs kind of nuts.

I saw an example of this shortly after I spoke to the Harts. While on a walk with Moose in some woods, I ran into a couple with a young female pit bull. They were lost, trying to find their way out of an unmarked labyrinth, and stopped to ask for directions. As I was telling them where to go, Moose, who tends to be shy (and, I always thought, preferred the company of males), was uncommonly interested in their bitch. He was straining against his leash, and it took all my strength to hold him back. “She’s in heat,” the couple told me as Moose sniffed her like a steak. That explained it. 

“Well,” I thought as I dragged him away. “I guess he’s straight.” 

This type of behavior is certainly something to consider when weighing whether or not to desex your dog. Moose has never run away but I do occasionally take him off-leash on trails and in parks. He always stays close and returns when I call him, but if we encountered a dog in heat while he was off-leash, I could not guarantee he wouldn’t try to make puppies. He’s an animal, and that’s what animals do. Did that mean off-leash was over? I made a mental note to add a tick to my Cut Moose’s Balls Off list. 

And yet, while there is anecdotal evidence that spaying and neutering may calm your dog down, studies also show that neutering can make your dog behave worse. 

James Serpell, the director of the Center for the Interaction of Animals & Society at the University of Pennsylvania, developed the Canine Behavioral Assessment & Research Questionnaire, a survey about dog behavior for pet owners and trainers. Since its inception in 2005, Serpell and his team have collected data on over 50,000 pet dogs and their behaviors, including things like aggression, fear, anxiety, attachment, and excitability. (Moose, I am proud to say, got nearly perfect scores, although he was marked down for barking at the mailman.)

After analyzing this data for differences in dogs that had been spayed and neutered, “We found very dramatic differences in male dogs,” Serpell told me. But here is the surprising part: “Nearly all of those differences were bad. The neutered animals had less good behavior on 26 variables. That was a bit of a surprise since it seemed to go against what everyone was saying.”

These variables included aggression, fearfulness, and excitability. Spayed and neutered dogs, contrary to common belief, were also rated less trainable than their intact counterparts.

Serpell and his team did the same analysis with female dogs, and while the effect wasn't quite as dramatic, there were still at least six variables in which spayed females seemed to perform worse, especially when the procedure was done early. 

Still, Serpell told me, the data don’t show the whole picture, because if you look at dogs that are relinquished to shelters by their owners because of behavioral problems, intact male dogs are over-represented. 

“There's something going on, and my guess is that it's to do with an adolescent surge in testosterone that is causing people to relinquish their teenaged male dogs that are suddenly starting to show obnoxious behavior,” Serpell said.

And the behavior can be really obnoxious. While Moose (thank god) seems to have a low sex drive and only occasionally humps my leg (always when I’m on the phone, for some reason), I’ve heard stories. One friend told me she got her dog neutered because he was leaving “deposits” on her husband’s pillow every morning. The writer Meghan Daum, who has written beautiful essays about her life with Newfoundlands, told me on her podcast recently that her 165-pound puppy Hugo attempts to mount her daily, and if you’ve ever tried to tell a Newfoundland “no means no,” you’ll know they aren’t great with consent. Meghan was counting down the days until Hugo could get neutered. And while it’s no guarantee, neutering, in Hugo’s case, might help.

“Neutering could dampen some dog’s more... lascivious urges,” said Alexandra Horowitz, the director of the Dog Cognition Lab at Barnard College and the author, most recently, of Our Dogs, Ourselves. Horowitz has written about the spay and neuter dilemma as well, and she told me that her own male dogs were very excited to meet females in heat, even well after they were neutered. 

Luckily, many of the more annoying behaviors can dissipate on their own, whether or not you decide to neuter. Just like with humans, testosterone levels naturally deplete as dogs age, and the sex-craze can wane in adulthood. But I understood why Meghan was anxious to get Hugo fixed as soon as possible—how much dog humping can one person really put up with, especially from a giant?

As for why, exactly, dogs hump, plenty of dog owners (and trainers) will insist it’s not sexual, that humping is about dominance rather than sex. And this makes sense from the human perspective: We don’t like to think of dogs as sexual beings. Moose looks like a sentient teddy bear. Who wants to think about teddy bears having sex

But the idea that dogs mounting each other is more about dominance than sex, according to Horowitz, is wishful thinking. 

“It’s completely wrong,” she told me. “It’s not about dominance at all. It’s about using a sexual behavior in a playful way, and it would probably happen more often if people didn’t intervene.” 

She challenged me, the next time Moose gets mounted at a dog park, to just watch instead of intervening.

“It’s play,” she said. “They work it out.” 

Besides the possibility of unplanned puppies, I wondered if keeping Moose intact would make him more of a target for other dogs’ aggression. I’m not worried about Moose being aggressive—not only does he look like a teddy bear, he’s got the personality of one—but at about six months old, he’d been attacked by at a dog park. I asked Serpell if his nuts might have something to do with it. In short: maybe. 

“There's anecdotal evidence that intact males are more likely to be attacked by neutered males,” Serpell said. “We don't really know how reliable it is and it's unclear why that would be the case except perhaps that neutered males feel more threatened.”

Does this mean it’s not safe to take Moose to dog parks unless he’s neutered? Well, maybe. He’s only been attacked once, and he wasn’t actually hurt, but it’s certainly something to weigh when making this decision. Moose likes going off-leash. I like taking him to dog parks. Can I responsibly keep doing this if he keeps his nuts? Some dog parks don’t even let intact males in. But then, on the other hand, there are risks with desexing too. What’s worse? No dog parks or a higher risk of joint disorders and cancer? I’m honestly torn.

In an ideal world, these are the things vets would talk about with their clients. But instead, we’ve largely had a one-size-fits-all model, where the recommendation from most veterinarians, animal welfare groups, shelters, and the ASPCA has long been that all dogs, no matter the breed or the lifestyle, should get fixed. 

The Harts would like to see this model change.

 “We've argued for this new approach to neutering,” Ben said. “Veterinarians should sit down and talk with their clients. They explain what the data is so far and help that client arrive at a decision. It’s a paradigm shift.”

And the paradigm is shifting. The American Veterinary Medical Association now endorses individualized healthcare rather than across-the-board desexing, noting that “there is no single recommendation that would be appropriate for all dogs.” It may have taken a while, but the establishment is starting to listen to what the Harts have been saying.

So what’s going to happen to Moose’s nuggets? We’ll get to that in the final chapter of this series, and we’ll also explore some alternatives to traditional spaying and neutering that might just be the perfect solution. 

Moose Nuggets is free and available for all, but if you do feel like contributing to Moose’s college fund, I will gladly accept it on his behalf. If you have thoughts about dog de-sexing, I can be reached at or on Twitter @kittypurrzog.