The Truth About Spaying Dogs

Matt Kuenzel
10 min readAug 18, 2023

Spaying, or ovariohysterectomy, the surgical removal of the ovaries, fallopian tubes, and uterus is the grotesque, barbaric mutilation of a female dog. While the stated purpose is pregnancy prevention, that goal can be accomplished effectively by proper care of the female dog during her estrus cycle. Moreover, not all surgical approaches to sterilization require complete removal of the reproductive system. Simply tying the fallopian tubes (tubal ligation) is enough to prevent pregnancy.

Americans are notoriously squeamish about all things sexual. That attitude also informs their thinking about neutering dogs. Many people find the dog’s sexuality repulsive: the mortification of one’s dog sniffing, mounting, and humping another dog, or worse, a pillow or a guest’s leg, the panicky revulsion aroused by the thought of dog semen or menstrual blood on the furniture or carpeting; these thoughts are what make people susceptible to the idea that neutering their dog really is best for their dog, and, in a bit of good fortune, also curbs “nuisance” behaviors.

The institutions that benefit such as the veterinary industry reinforce the idea that responsible pet owners spay their female dogs. But it is considered sacrilege to mention that spaying grossly exceeds the minimum necessary intervention to prevent procreation and carries many serious negative effects on the dog’s health and well-being. As long as everyone repeats the mantra, “responsible pet ownership,” dog owners dare not defy the common practice, veterinarians benefit by standardizing on and selling one solution for all dogs, and the barbaric system continues.

But widespread neutering is not the default everywhere. In some parts of Europe, it is considered an unnecessary, or even cruel and abusive, intervention. One survey of German pet owners found only 43 percent of dogs are spayed or neutered. In Sweden, estimates are as low as 10 percent. Norway’s animal welfare prohibits neutering in most cases, although it allows exemptions if the surgery would improve the welfare of the animal. Dogs in these countries are left intact, and it is up to the owners to ensure that they do not mate.

Patrick Pageat, a French veterinarian, said that many people in France regard neutering in the same category as controversial procedures such as declawing a cat or cropping a dog’s ears.

“People [in France] are less and less keen to neuter animals. It is regarded as something close to abuse,” Pageat said. “It’s your duty as a responsible owner to make sure that you can control your dog. Neutering or spaying dogs is not a medical necessity.”

The ovaries are organs which produce the vital hormones that regulate the reproductive cycle but which also affect the urinary tract, the heart, blood vessels, bones, skin, mucous membranes, muscles, and the nervous system including the brain.

In humans, these hormones are vitally important for mood and well-being. It also keeps bones strong and healthy. Thus, problems like osteoporosis, lack of concentration, and mood swings arise during menopause. Ovary removal in human females was halted in the mid-1950s except for life-threatening medical reasons as it brought on “surgical menopause” which was deemed dangerous and unhealthy. That is exactly what spaying does to dogs.

For people who consider dogs to be living creatures with the same right to ethical treatment as human beings, the same principles should apply to their medical care. The first consideration must be the welfare of the dog. Although we cannot know the preferences of dogs, we can use the principles of human care as a guide.

Those principles require that all medical treatments must be necessary to the health or survival of the patient, human or dog. The convenience of others, the reduction of nuisance behaviors, is not a valid reason to massively alter the biology of a human or a dog.

But despite the simple clarity of that point, that spaying can only be justified if it’s necessary for the dog’s health or survival, there are still ongoing debates about the benefits vs the damage that spaying causes.

Among the most frequently cited benefits are a reduction in certain types of cancers, the most common of which are mammary cancers. However, the American College of Veterinary Surgeons has this to say on the topic, “More than a quarter of unspayed female dogs will develop a mammary tumor during their lifetime. The risk is much lower for spayed female dogs, male dogs, and cats of either gender. In female dogs, 50% of mammary tumors are benign and 50% are malignant. However, few of the malignant mammary tumors are fatal.”

Conversely, other types of cancers are more common in spayed female dogs including those of the heart, bone, spleen, and bladder.

Another frequently claimed benefit of spaying is a longer lifespan for spayed dogs. However, the relationship between spaying and a longer lifespan may be due to other factors associated with spaying, such as the fact that spayed dogs are more likely to seen by veterinarians, and it is impossible. Additionally, recent research finds that, “Ovaries are part of a system that promotes longevity.” (see full excerpt below)

The rest of this article will review some of the literature on the effects of spaying on female dogs.

from “Behavioural risks in female dogs with minimal lifetime exposure to gonadal hormones”
from “Behavioural risks in female dogs with minimal lifetime exposure to gonadal hormones”

Above: Negative percentage differences mean that the intact dogs were less likely to display the associated behavior. Positive percentage differences mean that the intact dogs were more likely to display the associated behavior.


In 2009, after carefully studying the association between the number of
years of lifetime ovary exposure and highly successful aging in Rottweilers,
we discovered that keeping ovaries longer is associated with living longer [6]. This link between ovaries and longevity was independent of lifetime
investment in reproduction [7], as well as cause of death or familial longevity [6]. Our work pointed to a new line of thinking: Ovaries are part of a system that promotes longevity. This transformational way of thinking — seeing ovaries not just as reproductive units but as healthspan-promoting endocrine organs — is now supported by newer research on the longevity-extending effects of ovaries in women and mice [8–12].

from “Behavioural effects of ovariohysterectomy on bitches”

Study Results

Significant differences were found between control and spay group dogs in dominance aggression and indiscriminate appetite. Spayed dogs were more likely to have an increase in dominance aggression towards family members between the first and second interviews compared with the control group, while the control group dogs were likely to have a decrease in this type of aggression. The spay group had an increase in indiscriminate appetite (eg, eating meals quickly, eating any commercial dog food, and ingesting other food-associated items such as trash) between interview one and two while the control group dogs had a decrease in this activity.

from “Behavioural risks in female dogs with minimal lifetime exposure to gonadal hormones”


This study corroborates results from the related study on behaviour in relation to exposure to gonadal hormones in male dogs, showing a similar increased likelihood of owners reporting fearful and aggressive behaviour in their dogs with decreased exposure to gonadal hormones.

from “An inconvenient truth on obesity and sterilization in dogs”

Risks: For females, pyometra (uterine infections) and mammary tumors are the biggest risk. All but the most aggressive mammary tumors are treatable, if caught early.

Benefits: Normal hormone levels may protect dogs from suffering from certain orthopedic diseases along with some cancers. In females, low sex hormone levels predispose them to hormone-related incontinence.

The inconvenient truth is that dog sterilization leads to fatter dogs. This we know. No one disputes it. Whatever you think about all these new studies on sterilization and certain diseases, the reality of the situation is this: Intact dogs are much more likely to enjoy healthy weights.

from “Vasectomy and ovary-sparing spay in dogs: comparison of health and behavior outcomes with gonadectomized and sexually intact dogs”

Our most important finding was that the longer duration that gonads were present, regardless of reproductive status, was associated with fewer general health problems and both problematic and nuisance behaviors. It was also associated with an increased lifespan.

from “Possible Relationship between Long-Term Adverse Health Effects of Gonad-Removing Surgical Sterilization and Luteinizing Hormone in Dogs”


Spaying and neutering dogs is commonly used to prevent the birth of unwanted animals. However, spaying and neutering is associated with an increased risk of several long-term health problems including obesity, urinary incontinence, bladder stones, hypothyroidism, diabetes mellitus, hip dysplasia, cruciate ligament rupture, behavioral changes (including owner-directed aggression and fear), cognition problems, as well as several forms of cancer (including leukemia, prostate cancer, bone cancer, skin cancer, splenic cancer, and bladder cancer). An explanation of how spaying and neutering increases the risk of these long-term health problems is discussed in this review.

from “Age at gonadectomy and risk of overweight/ obesity and orthopedic injury in a cohort of Golden Retrievers”

This study presents prospectively acquired data demonstrating that gonadectomy is a risk factor for both overweight/obesity and chronic non-traumatic orthopedic injuries in a prospective cohort of Golden Retrievers.

from “Long-Term Health Effects of Neutering Dogs: Comparison of Labrador Retrievers with Golden Retrievers”

In Labrador Retrievers, where about 5 percent of gonadally intact males and females had one or more joint disorders, neutering at less than 6 mo. doubled the incidence of one or more joint disorders in both sexes. In male and female Golden Retrievers, with the same 5 percent rate of joint disorders in intact dogs, neutering at less than 6 mo. increased the incidence of a joint disorder to 4–5 times that of intact dogs. The incidence of one or more cancers in female Labrador Retrievers increased slightly above the 3 percent level of intact females with neutering. In contrast, in female Golden Retrievers, with the same 3 percent rate of one or more cancers in intact females, neutering at all periods through 8 years of age increased the rate of at least one of the cancers by 3–4 times. In male Golden and Labrador Retrievers neutering had relatively minor effects in increasing the occurrence of cancers. Comparisons of cancers in the two breeds suggest that the occurrence of cancers in female Golden Retrievers is a reflection of particular vulnerability to gonadal hormone removal.

My Emphasis:

Neutered female labs had slightly higher rates of cancers than intact female labs.

Neutered female golden retrievers had 3–4 times higher rates of cancers than intact female golden retrievers.

from “What Are The Viable Alternatives to Spay and Neuter”

OESTROGEN: An extremely powerful female sex hormone that regulates many aspects of our life. This hormone plays a vital role in mental and physical health. It is also present to a lesser extent in male dogs. There are oestrogen receptors in bones, the brain, blood vessels, and the central nervous system.

PROGESTERONE: One of the female sex hormones also produced by the ovaries, also in the adrenal glands in male dogs. It aids immunity and can reduce inflammation and swelling; it also helps regulate the thyroid gland and keeps blood-clotting levels at normal levels. It has also been linked to forming social bonds in humans and animals.

from ChatGPT

What effect does loss of the ovaries have on cognition?

The effects of ovary removal (as occurs in spaying) on cognition in animals, particularly dogs, is an area of ongoing research and isn’t fully understood. The ovaries produce several hormones, including estrogen, which have been shown to have effects on the brain and cognition. Here’s what we know based on current knowledge:

1. Estrogen and Cognition: Estrogen has neuroprotective effects and plays roles in synaptic plasticity, memory, and cognition. In humans, for instance, the decline in estrogen levels during menopause has been associated with cognitive decline or changes in some individuals, though the relationship isn’t straightforward.

2. Animal Studies: Research on rodents has shown that estrogen can enhance cognitive performance on specific tasks, influence neurotransmitter systems, and promote neuronal growth and survival.

3. Canine Cognitive Dysfunction (CCD): This is a condition in older dogs that’s similar to Alzheimer’s disease in humans. Symptoms include disorientation, disrupted sleep patterns, house soiling, and changes in interactions with owners or other pets. Some research suggests that early spaying might be a risk factor for CCD, but the evidence isn’t definitive.

4. Neurological Changes: Studies on rodents have found that those without ovaries (due to ovariectomy) showed decreased dendritic spine density in the hippocampus, a brain region vital for memory. Estrogen replacement could reverse these changes, suggesting that the ovarian hormones play a role in maintaining certain brain structures.

from “Effect of gonadectomy on subsequent development of age-related cognitive impairment in dogs”

Conclusions and Clinical Relevance — Results suggest that the presence of circulating testosterone in aging sexually intact male dogs may slow the progression of cognitive impairment, at least among dogs that already have signs of mild impairment. Estrogens would be expected to have a similar protective role in sexually intact female dogs; unfortunately, too few sexually intact female dogs were available for inclusion in the study to test this hypothesis. There may be a need to evaluate possible methods for counteracting the effects of loss of sex hormones in gonadectomized dogs.

from “Effect of sex and gonadectomy on dogs’ spatial performance”

The present study sought to determine the role of biological sex and of gonadectomy on spatial learning, memory and reversal learning in pet dogs. Intact females were overall more successful, as 81% of them successfully completed the whole procedure, compared to 56% of spayed females, and to 62% of intact and 50% of castrated males. In terms of performance, the spatial learning task evidenced the largest differences amongst experimental groups, as intact females were faster in learning and more.