Scholarly article on health effects of spaying a dog

Question

Today I've been told by the vet to consider spaying our almost 3-year-old Jindo dog. We haven't spayed the dog for four reasons:

1. A while back, doing some light research on google (meaning I only read the first few search results) revealed that spaying brings on its own set of problems, and haven't found any article, particularly scholarly ones, that pushes the spaying from "recommended" to "you must."
2. I just find it hard to that the product of evolution has resulted in a species with so many health issues. While a lot of modern dogs, specifically those from "developed" nations have been bred for particular traits over generations, sometimes resulting in overbreeding that results in over-elongated dachshunds or snore-y pugs, Jindo dogs, from my understanding, haven't gone through such human intervention and simply followed the "survival of the fittest" rule.
3. My dog, without much effort on my part, has been healthy: she eats well, walks well, runs well, inhibits healthy squirrel chasing dog behaviors, and stays trim all on her own. At the very minimum, I walk her 40 mins a day to up to an hour every day. So far, she's seen three different vets in three different places we have lived, and they all said she is healthy. Combined with reason #2, I find it hard to believe that such a healthy dog would just start to develop problems because such problems are inherent to the species.
4. Lastly, I don't want to alter her in any way unless necessary. It's a medical procedure, and we're messing with biology. More than anything, it's an ethical issue; my dog may not be able to talk, but she has a right to her own body. Barring any medical emergency, I want to respect that right.

I hope I don't come across as some fringe anti-vaxx, flat-earther kind of person by expressing my skepticism about the generally accepted practice of spaying and neutering. My view is partly tinged by the fact that I know vets and animal shelters recommend it for the reason of controlling the animal population. (my dog is leashed 100% of the time she's outside, except on rare occasions when we go to the dog park, which we don't go unless we're 100% convinced that she's not in her heat cycle).

All that is to ask: where can I find some definite, credible statistics on the health effects of spaying dogs? I know it's hard to find articles on such a generic topic, so if I can get some sources on the effect of spaying on breast cancer, or some other major life-threatening issues in intact dogs, I'd really appreciate it.

According to this article (https://onlinelibrary.wiley.com/doi/full/10.1111/j.1748-5827.2011.01220.x, in the conclusion), this issue apparently isn't as studied as much as the rate of recommendation would have you believe.

Answer 1

Pro Spaying:

The opening phrase of the study "Effect of Spaying and Timing of Spaying on Survival of Dogs with Mammary Carcinoma" is the reason why most vets advice spaying female dogs:

The risk of developing mammary gland tumors in dogs is significantly decreased by ovariohysterectomy at an early age.

It furthermore states:

Signalment, spay status and spay age, tumor characteristics, treatment, survival, and cause of death of 137 dogs with mammary gland carcinoma were analyzed. The dogs were classified into 3 groups according to spay status and spay time: intact dogs, dogs spayed less than 2 years before tumor surgery (SPAY 1), and dogs spayed more than 2 years before their tumor surgery (SPAY 2). Dogs in the SPAY 1 group lived significantly longer than dogs in SPAY 2 and intact dogs (median survival of 755 days, versus 301 and 286 days, respectively, P= .02 and .03). After adjusting for differences between the spay groups with regard to age, histologic differentiation, and vascular invasion, SPAY 1 dogs survived 45% longer compared to dogs that were either intact or in the SPAY 2 group (RR = .55; 95% CI .32–93; P= .03). This study reveals ovariohysterectomy to be an effective adjunct to tumor removal in dogs with mammary gland carcinoma and that the timing of ovariohysterectomy is important in influencing survival.

Pro and Contra Spaying

The relationship of urinary incontinence to early spaying in bitches:

It is still controversial whether a bitch should be spayed before or after the first oestrus. It would be desirable to spay bitches at an age that would minimize the side effects of neutering. With regard to the risk of mammary tumours, early spaying must be recommended because the incidence of tumours is reduced considerably. The aim of the present study was to determine whether early spaying also reduces the risk of urinary incontinence.
[...]
Urinary incontinence after spaying occurred in 9.7% of bitches. This incidence is approximately half that of spaying after the first oestrus. Urinary incontinence affected 12.5% of bitches that were of a large body weight (> 20 kg body weight) and 5.1% of bitches that were of a small body weight (< 20 kg body weight). The surgical procedure (ovariectomy versus ovariohysterectomy) had no influence on the incidence, or on the period between spaying and the occurrence of urinary incontinence.
[...]
However, compared with late spaying the clinical signs of urinary incontinence were more distinct after early spaying.

The Effects of Spaying and Neutering on Canine Behavior:

Spaying of the female dog removes the source of estrogen and progesterone.Estrogen and progesterone are increased or decreased in cycles.
[...]
The most notable problem arises when the dog guards items maternally. Other problems can involve irritability, conflict with other dogs and energy reduction. “Guarding toys,dolls, rags, slippers or anything else that can be carried is another common behavioralconsequence of the surge in progesterone.”
[...]
Female dogs are at increased risk of disease if they are allowed to experience theirfirst heat. For this reason it is often suggested that a female dog be spayed prior to 6months of age. It would appear that dogs who demonstrate control complex aggression(aka dominance aggression) toward owners prior to 6 months of age are at risk forbecoming more aggressive after ovariohysterectomy. If a dog demonstrates a significantpropensity to control complex aggression it may be wise to avoid spaying these dogs.

Contra Spaying:

Spaying‐induced coat changes found that spaying can lead to negative changes in the fur:

Although spaying can result in qualitative hair coat changes in dogs, the influence of spaying on the hair growth cycle has never been described. [...] Spaying resulted in increased plasma gonadotropin concentrations and increased anagen : telogen ratio of hair follicles, but only 20% of the dogs developed coat changes.

---

A bit of general advice: If you're searching for scientific papers or articles, use https://scholar.google.com/ instead of the "normal" google search.

Answer 2

Here's my counter arguments, for what it is worth:

Regarding your thoughts on points one and three. Yes, there can be problems associated with spaying. These sorts of complications are also fairly uncommon. Spaying is a very common, routine procedure. Meanwhile, there are also many health risks associated with not spaying the animal. Such as pyometra (which is painful and potentially fatal, the risk increases greatly with age, and is treated by removing the uterus anyways), mammary tumors, tumors of the reproductive system, accidental pregnancy, any complications that arise from accidental pregnancy, and so forth. These things can happen randomly to an otherwise perfectly healthy dog. Do not take your dog's good health now to mean something couldn't randomly change later. I would speak to a vet about the health repercussions of spaying versus not, because they, being the experts, can speak to this in much more detail.

For the second point, I don't mean to be critical, but you are wrong. For one thing, all dog breeds are the product of selective breeding to some degree. You can tell by the fact that dogs have different reproductive cycles from wolves, where wolves only have one litter a year, and dogs (with the exception of the basenji) are capable of more than one.

Furthermore, evolution is not about "perfection," but rather what works well enough. Take, for example, the fact that birth in humans before modern obstetrics had an extremely high mortality rate due to the size of a baby's head versus the strange structure of human hips in order for us to walk upright, such that giving birth is generally much more risky for humans than animals. A baby's head must even rotate ninety degrees while passing through the birth canal in order to be able to fit. Women also have a huge range of medical issues that can be the indirect result of their never having been pregnant, or could possibly be corrected by a hysterectomy, like endometriosis or pcos, though many women choose not to.

As for the fourth point, everyone must choose where to draw their own lines, but an animal cannot consent, and furthermore, as a pet owner, you will always have to make the choice of "violating the animal's right to its own body" versus doing a medical procedure that is necessary for the animal's greater well being. Even taking the animal to the vet is "violating its consent" as the vast majority of animals very obviously hate being handled by the vet. We do these things because we are responsible for the well being of the animal, and animals are incapable of understanding enough to make that choice. There are many compelling health reasons why I think you should choose to spay your animal, and therefore, I see it as fitting into the category of "violating consent" for its greater well being.

Lastly, you should take the concern of unwanted puppies into consideration, as you would also be responsible for their well being, and where they are ultimately homed.