Spay & Neuter

For most behaviors, spaying/neutering was associated with worse behavior, contrary to conventional wisdom.
— Effects on Behavior By Dr. Deborah Duffy
  • Early Spay & Neuter

  • Behavior Problems

    • Aggression

    • Fearful Dogs

  • Research update: Earlier age at spay/neuter a risk factor in orthopedic injuries

  • Behavioral Considerations of Spay & Neuter

  • Health Risks of Spay and Neuter

  • Alternatives to Traditional Spay/Neuter

  • Research

Early Spay & Neuter

Early spay and neuter in the USA is a common method to control over population. But research now has many questioning whether early spay and neuter is harmless and the best procedure for population control. Another reason given for early spay and neuter is to avoid potential health problems like mammary tumors, and ovarian or testicular tumors. While early spay and neuter has been shown to reduce risks of mammary tumors there is a growing body of research that reflects an increase risks with other serious health problems some of which are: osteosarcomas, hypothyroidism, orthopedic problems,  and age-related Cognitive Dysfunction to list a few.

It was not that long ago that “vestigial structures and organs” were thought to be useless or close to useless because medical science lacked a full understanding of them. A similar scientific understanding of the canine body continues to grow with more knowledge of the function of various body parts. Many are now recommending a sterilization procedure that preserves normal endocrine function which is important for growth and development.

Noise Sensitivities in Dogs: An Exploration of Signs in Dogs with and without Musculoskeletal Pain Using Qualitative Content Analysis

“In this study, concerns over musculoskeletal problems were confirmed using a range of procedures (some individuals having multiple procedures): four clearly demonstrated pain during physical examination in the clinic, eight were radiographed, and one underwent magnetic resonance imaging. The problems identified or inferred related to the hip (including dysplasia–five subjects), degenerative joint disease of the limbs (four subjects), and focal spondylosis in L2 and L3 (one subject). In six of these cases, the owner commented that the dog seemed to be in some pain and/or the pain worsened after exercise.”

“There was a large proportion of neutered dogs: 9 of 10 of both controls and “clinical cases,” whereas the Pet Animal Welfare Report (29) suggests that nationally only about 71% of dogs are neutered. A study by Spain et al. (30) found that decreasing age at gonadectomy in shelter dogs was associated with an increased risk of developing a noise phobia, but it could not be concluded that neutering is causative of noise phobias.”

Modernizing spay practice for females

Hormone-sparing Male Sterilization


Many people hope that spaying or neutering will help to calm their dog, or resolve or prevent behavior problems in the future. This is an unreasonable expectation since most behavior is prone to environmental influences and not due to the result of circulating hormones.  The one behavior that spaying and neutering does impact is that of unneutered male dogs who are motivated to escape and roam to get to a female dog in season. Female dogs that are unspayed will attract male dogs from great distances when they are in season. Neutering a male dog will remove the frustration, motivation and attraction to females in season.

Genetics and previous learning gives opportunities for behavior to develop, but the environment gives the dog the opportunities to practice a behavior and determine its intensity. A dog’s behavior is influenced by four things. Genetics, early learning, the current environment, and the humans it lives with.  A dog’s behavior is based on what they have been taught/learned/or fear of the unknown, or its predicated on what they have been permitted to do.  Understand we don’t “fix” normal. We should not be surprised that a guarding breed has guarding tendencies, or a herding breed has herding tendencies or likes to control space, or terriers like to chase small critters, or that sporting breeds (gun dogs) often pickup things and carry things in their mouth.  A dog can have tendencies to bark, guard, chase, and urine mark places. But what a trainer looks to identify is whether a dog’s training has been developed for your dog, its breed type, that will give you control over those instincts. Or whether the training was designed to make sure those instincts are completely out of control.  Some training is commission based, and other is omission based.

Those things practiced become habits that are hard to break.  A dog inclined to bark does not have to be an incessant barker. A guarding breed should permit people you invite into the home without reacting. A dog that likes to chase should be trained only to chase in your presence when given permission. How does the dog perceive their role within the environment and what are the dog’s expectations of how to behave? Dogs should be responsible to you, not for you. If your dog acts as if it is responsible for you, you will lack control over your dog’s behavior.  Spaying and neutering should not be expected to resolve behavior problems. This is a function of training and having the right relationship with your dog.

Effects on Behavior By Dr. Deborah Duffy

Effects of ovariohysterectomy on reactivity in German Shepherd dogs

Neutering: What’s Behaviour Got To Do With It?

Neutering Risks and benefits: Bitches

The timing of spaying may have an affect on aggression.

“The calming effect of the high level of progesterone is also the reason why it is best to avoid spaying bitches for two months after estrus. Spaying during this time can result in a precipitous drop in progesterone levels with possible accompanying emotional disturbances, irritability, aggression and depression.”   The Dog’s Mind  By Bruce Fogle, D.V.M., M.R.C.V.S.      

“Progesterone has calming influences, and because spaying removes the source of progesterone production, causing a precipitous fall in progesterone may increase irritable tendencies in young females. After a female has gone through some estrus cycles, and possibly been disciplined for aggressive behavior, the spaying may have less of an impact.”    Canine and Feline Behavior Therapy   Second Edition  By Benjamin L. Hart, Lynette A. Hart, Melissa J. Bain 

“Hart and Eckstein (1997) point out that female dogs are in a progestational state for 2 months following an estrus period and spaying them during that period creates a sudden removal of the source of progesterone (which tend to have a calming influence on animals). It is postulated that this removal of progesterone may promote irritability or aggression in some individuals.”    Aggressive Behavior In Dogs    By James O’Heare 

For help with Aggression Problems


Early spay and neuter is not believed to be the cause of these issues but it’s reasonable to believe that it contributes to fear aggression. If a dog is fearful my approach would generally be to wait on sterilization until the dog has built a solid foundation of trust with people. Imagine it from the dog’s perspective. You lack confidence, you don’t fully trust people, and you are taken to a place with strangers, people you don’t trust, or infrequent acquaintances and you wake up in a strange place, scared, injured, and in pain. This experience has a way of confirming what you believed all along and can lead to more serious problems. 

By Dr. Karen Shaw Becker

The vast majority of veterinarians, conscientious pet parents and dog advocates across the U.S. sincerely believe the best thing we can do for our canine companions is spay or neuter them at an early age.

Conventional wisdom holds that dogs must be desexed to avoid diseases of the reproductive organs, as well as to avoid adding to pet overpopulation. This belief is so firmly entrenched in our American culture that pet owners who don’t spay or neuter are considered irresponsible and deserving of scorn.

In veterinary school, students are taught to promote desexing surgery to every pet parent, and the only procedures they learn are full spays and neuters, which desex (remove animals’ ability to produce sex hormones) as well as sterilize (prevent reproduction).

By the time I opened my own animal hospital after veterinary school, I’d been volunteering at a kill shelter for 10 years as a euthanasia technician, and I was adamant that my clients spay or neuter. I desexed thousands of pets when they were very young, convinced I was carrying out my moral obligation as an ethical veterinarian.

The Decision to Perform Spay/Neuter Is Often Based on Convention, Habit or Misconception of Health Benefits

Unlike when I first started out as a veterinarian, today we can refer to a steadily growing body of scientific research that indicates spay/neuter has a significant downside for dogs.

“ … [A]s we’re now learning,” writes veterinarian Dr. Patty Khuly in an article for Veterinary Practice News, “preventing reproductive disease isn’t necessarily a good enough reason to remove organs; not if those organs offer more benefits than they pose risks.”1

In a report for Clinician’s Brief, Dr. Clara Goh, surgical oncologist at Colorado State University’s Veterinary Teaching Hospital states:

“The decision to perform this procedure [spay or neuter] is often based on convention, habit, or misconception of health benefits rather than on an evidence-based assessment of each patient.”2

After I’d been in practice about five years, I started connecting the dots when many of my spayed and neutered patients began to develop endocrine issues. After some research and soul searching, I realized I was insisting on desexing my patients not based on what was physiologically best for them, but rather what I felt was morally best for their owners.

I went through an extended period of feeling overwhelming guilt and the need to apologize to both my clients and patients. I also began changing my recommendations on spaying and neutering.

Risks and Benefits of Spay/Neuter on Large and Giant Breed Dogs

Over the last several years, a number of small, breed-focused, primarily retrospective studies have been conducted on the effects of spay/neuter in large and giant breed dogs, including the Rottweiler and Golden Retriever. Goh of CSU provides the following information to illustrate what the research has uncovered about the potential benefits and adverse effects of gonadectomy:

Condition                                       Effect of Spay on Female Large/Giant Breeds               Effect of Neuter on Male Large/Giant Breeds

Overall longevity                                   Mild increase                                                                   Mild increase

Obesity                                                Moderate increase                                                           Moderate increase

Cranial cruciate ligament disease          Moderate increase*                                                         Moderate increase*

Hip dysplasia                                        Mild increase*                                                                 Mild increase*

Mammary tumors                                  Marked decrease*

Uterine, ovarian, vaginal tumors            Prevents

Testicular tumors                                  —                                                                                   Prevents

Perianal gland tumors                          —                                                                                    Market decrease                                

Prostatic carcinoma                            ----------                                                                             Prevents                                           

Lymphoma                                         Mild increase                                                                     Mild increase*

Mast cell tumors                               Mild increase                                                                       —

Hemangiosarcoma                            Mild increase*                                                                      Mild increase

Osteosarcoma                                 Mild increase*                                                                      Mild increase*

Transitional cell carcinoma               Mild increase                                                                       Mild increase

Urinary sphincter mechanism incompetence     Moderate increase*                                              —

Cystitis                                           Mild Increase*                                                                      —            

Benign prostatic hyperplasia             —                                                                                       Marked decrease        

Perineal hernia                                                                                                                              Moderate decrease

*Age at time of surgery may be important

To summarize the above information: Spaying or neutering large and giant breed dogs decreases or prevents most reproductive organ disease, as you would expect, since conventional desexing surgery removes some or all of those organs and the hormones they produce.

The diseases for which spayed or neutered dogs are at increased risk are, as you also might expect, some of the most common disorders seen in dogs today. They include obesity, cranial cruciate ligament (CCL) ruptures, hip dysplasia, several types of cancer, urine dribbling (incontinence) and cystitis (bladder inflammation).

The Risk of Obesity Is Increased in Spayed and Neutered Dogs

It’s worth noting that obesity in pets is at epidemic levels. In 2017, 56 percent of dogs were overweight or obese, and Khuly believes spay/neuter has played a significant role in the explosion of fat dogs over the last few decades.

“To be sure, it has a lot to do with how we feed ourselves and our families and the ‘food is love’ culture we reside in,” she writes. “It also has a lot to do with the rise of the pet food industry and the proliferation of diets and treats it so effectively markets. But could there be another component we conveniently tend to overlook? After all, everyone knows for sure that spayed and neutered dogs are heavier.

There’s no doubt about it. 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.”

Khuly addresses some great questions to her veterinary colleagues:

  • Is spaying and neutering our dogs actually healthier for them?

  • Have we been led astray in our thinking on this issue by our community’s desire to prevent pet overpopulation?

  • Are veterinarians actually recommending what’s best for our individual dogs?

  • Have we researched this issue well enough given our level of sophistication on so many other veterinary issues?

Khuly believes the health of dogs and the problem of pet overpopulation are two separate issues and should be view as such.

“After all,” she writes, “sterilization is not required to achieve normal population levels. In fact, in Europe, for example, where spaying and neutering isn't common, there is no dog overpopulation problem (and, incidentally, a much reduced incidence of canine obesity compared to U.S. dogs).”

Khuly hopes “… responsible Americans are completely capable of keeping their pets from breeding just like Europeans do.” But she laments that every time she brings up the subject, she gets “… lambasted by loud-voiced zealots who claim [she’s] irresponsibly encouraging pet overpopulation by suggesting there may be alternatives to sterilization.”

“… [U]ntil we … stop talking about overpopulation and sterilization in the same breath,” she concludes, “we’ll have to face the inevitable reality: Our dogs are fat, and they’re destined to get fatter. Perhaps one day we’ll be able to look at this problem more dispassionately, but until then, I expect to continue to see more obesity-related disease in dogs than almost any other medical condition.”

Khuly makes a good point about the connection between obesity in dogs and spay/neuter practices, and in general, I’m really happy to see an article like hers in a publication whose audience is primarily the conventional veterinary community. That said, I think of all the risks associated with spay/neuter, overweight and obesity are entirely preventable when pet parents are committed to keeping their dog at a healthy weight.

Some Things to Think About if You’re Considering Spaying or Neutering Your Dog

Dr. Becker

As I mentioned earlier, over the years I've changed my view on spaying and neutering dogs, based not just on a mounting body of research, but also on the health and behavior challenges faced by so many of my canine patients after I desexed them. That’s why my current approach is to work with each individual pet owner to make decisions that will provide the most health benefits for the dog.

Whenever possible, I prefer to leave dogs intact. However, this approach requires a highly responsible pet guardian who is fully committed to and capable of preventing the dog from mating (unless the owner is a responsible breeder and that's the goal).

It’s important to note that I'm not advocating the adoption of intact shelter animals to people who may or may not be responsible pet owners. Shelter veterinarians don't have the time or resources to build a relationship with every adoptive family, so the animals in their care must be sterilized prior to adoption to prevent more litters of unwanted pets.

My second choice is to sterilize without desexing. This means performing a procedure that will prevent pregnancy while sparing the testes or ovaries so they can continue to produce hormones essential for the dog's health and well-being.

This typically involves a vasectomy for male dogs, and either a tubal ligation or modified spay (a hysterectomy) for females. The modified spay removes the uterus while preserving the hormone-producing ovaries. It also eliminates the possibility of pyometra because the uterus is removed.

Rarely, older, intact male dogs develop moderate to severe benign prostatic hyperplasia (an enlarged prostate) that may be improved with conventional neutering. Generally speaking, mature intact dogs have had the benefit of a lifetime of sex hormone production, so the endocrine imbalances we see with spayed or neutered puppies don't occur when dogs are desexed in their later years.

Unfortunately, veterinary schools in the U.S. only teach full spays and neuters, so unless your own vet has obtained additional training in sterilization techniques that spare the ovaries or testicles (which is unlikely), you’ll have only one surgical option available to desex your pet.

In that case, my suggestion is to wait until your dog has reached full musculoskeletal maturity, and if you have a female, I’d also wait until she’s completed her first estrus cycle before scheduling the surgery. Thankfully, the Parsemus Foundation maintains a list of veterinarians who perform vasectomies and hysterectomies (ovary-sparing spays) — click here to see if there’s a vet in your area.

  Providers of alternatives to traditional spay/neuter

 This list is provided as a service to individuals seeking a veterinarian willing to perform procedures beyond surgical spay or neuter. Veterinarians are added at their request, and Parsemus Foundation does not endorse any veterinarian. If you are a vet who would like to be included, please contact us at


Effects on Behavior By Dr. Deborah Duffy

Non reproductive Effects of Spaying and Neutering

Behavioural risks in male dogs with minimal lifetime exposure to gonadal hormones may complicate population-control benefits of desexing

Neutering: What’s Behaviour Got To Do With It?

Effects of ovariohysterectomy on reactivity in German Shepherd dogs

Behavioral and Physical Effects of Spaying and Neutering Domestic Dogs  (Canis familiaris)

Aggression toward Familiar People, Strangers, and Conspecifics in Gonadectomized and Intact Dogs

SPAY NEUTER and excellent article from Repawsitory

Health Risks of Spay and Neuter

“Dogs who've been spayed/neutered have more CCL damage than intact animals, which makes sense since sex hormones appear to have a protective effect on the musculoskeletal system.”

While gonadectomized dogs experience a zero risk of ovarian or testicular cancer and a lowered risk of benign prostatic hyperplasia and anal gland adenocarcinomas, there is mounting evidence that gonadectomy significantly increases the risks of developing many different serious forms of cancer, including hemangiosarcoma, mast cell cancer, prostatic carcinoma, osteosarcoma, and lymphoma/ lymphosarcoma, along with the development of these cancers at earlier ages (44–55). This increased risk of cancer may be related to the long-term effects of elevated blood levels of luteinizing hormone (LH) (56). LH binds to receptors on many tissues throughout the body; this reaction stimulates a number of cellular processes including cell division and nitric oxide release. In addition, gonadectomized dogs have increased risks of a number of orthopedic diseases, including cranial cruciate-ligament insufficiency, hip dysplasia and patellar luxation (44–46, 57–61), and also of numerous autoimmune diseases (62).

Non-Reproductive Long-Term Health Complications of Gonad Removal in Dogs as Well as Possible Causal Relationships with Post-Gonadectomy Elevated Luteinizing Hormone (LH) Concentrations

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

Why I've Had a Change of Heart About Neutering Pets

Neutering Dogs: Effects on Joint Disorders and Cancers in Golden Retrievers

Endogenous Gonadal Hormone Exposure and Bone Sarcoma Risk (Rottweiler)

Exceptional longevity in female Rottweiler dogs is not encumbered by investment in reproduction

Gonadectomy effects on the risk of immune disorders in the dog: a retrospective study

Determining optimal age for gonadectomy in the dog: a critical review of the literature to guide decision making

Health Risks of Spay and Neuter

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