Hormone-Sparing Sterilization

An adult Golden Retriever for Hormone-Sparing Sterilization

Project Summary: Hormone-Sparing Sterilization

Promoting choice for optimal animal health

Spaying and neutering pets to reduce pet overpopulation is standard veterinary practice, and usually involves removal of the sex organs to sterilize the animal. More recent research on dogs has shown that the lack of natural hormones resulting from spay/neuter can lead to other serious health complications. Hormone-sparing methods — like hysterectomy (also called ovary-sparing spay) for females and vasectomy for males — are ways to sterilize pets without the negative impacts from hormone loss.

Handy Resources:

Veterinarian Directory

Looking for a veterinary clinic to perform ovary-sparing spay or vasectomy? Find a local clinic in our Veterinarian Directory ›

  • Dogs, cats and other pets reproduce very quickly, producing thousands of animals in only a few generations.
  • Pet sterilization is necessary in most countries to keep population levels under control. In the U.S., spay and neuter has become standard practice and is completed by removal of the sex organs – the ovaries and uterus in females (ovariohysterectomy) and the testes in males (orchiectomy or castration).
  • After several decades of widespread spay/neuter practice, research in dogs has found that removal of the sex organs and associated hormones can result in significant health issues for some pets, including cancers and orthopedic problems.
  • Sterilizing dogs while retaining natural hormones is a way to address population concerns without the negative health impacts from hormone loss.
  • The Parsemus Foundation is proposing that we all think more creatively about individualizing pet sterilization, as is recommended by the Society of Theriogenology.
  • Hormone-sparing sterilization options, including ovary-sparing spay (hysterectomy), vasectomy, and intra-epididymal calcium chloride injection, can enhance the lifelong well-being of pets while maintaining population control.
  • Educating pet owners on the potential health and behavior problems associated with spay and neuter, and encouraging the availability of hormone-sparing sterilization options, is being achieved through website resources, public presentations, research, and maintenance of a veterinary directory of providers.

Project Topics

A bit of history on pet sterilization

Spay or neuter surgery (called gonadectomy because it removes the gonads) is considered standard care to prevent unwanted puppies in the United States and some other countries. But most people do not realize that this practice is relatively new and not common practice across the world.

Pet overpopulation in the U.S. grew in the 1960s and spay/neuter clinics opened in the 1970s to provide low cost/high volume sterilization service. Animal protection organizations supported widespread spay and neuter programs and lobbied for stricter regulations on licensing, control and sterilization of pets. By 2010, a majority of states in the U.S. had mandatory spay/neuter laws to address the homeless pet population. In most U.S. states, animal shelters are required to sterilize dogs and cats prior to releasing them.

Spaying and neutering dogs and cats – along with other methods to encourage responsible pet ownership – helped to reduce pet overpopulation and euthanasia by the 1980s. Over 80% of dogs in the U.S. are spayed or neutered. The practice of neutering pets varies greatly across the world, and in some cultures, it may be considered cruel or harmful. See this publication for more background and references on the history of spay and neuter – and the growing demand for hormone preserving methods of pet sterilization.

What’s wrong with spaying and neutering pets?

Have you had a beloved dog that suffered from cancer or a cruciate ligament tear? You might be surprised to know that a number of serious health conditions like these are more common in dogs that have been spayed or neutered.

Spay and neuter became a standard of veterinary practice and a tenet of “responsible pet ownership” to address the overpopulation of cats and dogs in the United States and other countries. But today, research has shown that removing the gonads (ovaries or testicles) is related to serious negative health and behavior outcomes in many dogs.

Various types of cancers, joint disorders, obesity, incontinence, fear/aggression, and immune diseases like diabetes may be more common in spayed or neutered dogs. Scientists are still studying this issue, but we do know that the chance of negative lifelong health problems due to loss of hormones is related to the dog’s sex, breed, age, and size. On the positive side, diseases associated with the gonads (like testicular cancer) are no longer a concern once they are removed by spay or neuter.

If you are making a sterilization decision for your pet, the Parsemus Foundation encourages working with a knowledgeable veterinarian to discuss the risks and benefits of different methods of sterilization for your dog. We provide a great deal of background data and references you can share with your veterinarian, too.

For more information on the health and behavior impacts of loss of hormones due to spay and neuter:

Loie, a perfect example of the dilemma

Abandoned at the rural shelter with her litter of puppies, Loie was a lab/rottweiler mix and just starting her second heat when a rescue organization saved her.  Remove her ovaries now? Spayed labs and rottweilers face particularly great health risks. The loss of hormones could quadruple her risk of bone cancer  and raise her risk of hemangiosarcoma to 10-20%. That’s not to mention the increased risk of CCL tears, incontinence, and weight gain common in these breeds. But what if she could have a hysterectomy and keep her ovaries (but still be sterilized) instead?

Rescued Dog Loie

Hormone-sparing sterilization: the healthy alternative

As more pet owners and veterinary practitioners have realized that spay and neuter surgery may have lifelong health implications for dogs, alternative options are becoming more common.

Female dogs

  • Hysterectomy removes the uterus and cervix but retains the ovaries, thereby sterilizing the dog while preserving hormones produced by the ovaries.
  • Female dogs who have had a hysterectomy have natural hormones, which means that they may show behavioral signs of the heat cycle once or twice per year, and may be attractive to males.
  • You might wonder why tubal ligation (which is common in humans) is not normally recommended for dogs. In this procedure, only the fallopian tubes are blocked, cut, or tied to prevent eggs from entering the uterus for fertilization. But about 25% of dogs get pyometra – a serious disease that affects the uterus and cervix and often requires emergency surgery. A hysterectomy that removes ALL the cervix and uterine tissue avoids the possibility of pyometra – a major advantage over tubal ligation.

Male dogs

  • Vasectomy for male dogs is a simple procedure in which the tubes that carry sperm (called the vas deferens) are cut or blocked.
  • Natural hormones produced by the testicles are maintained. Male dogs may be attracted to females in heat.

Nonsurgical methods

A number of nonsurgical sterilization methods have been evaluated, with varying levels of research on safety and effectiveness. Click the button below for more information.

Is hormone-sparing sterilization good for cats, too?

More cat parents want to know if the loss of natural hormones due to spay and neuter affect cats as well as dogs AND if hormone-sparing sterilization is a good choice. Unfortunately, research on the implications of hormone loss in cats is not yet advanced enough to evaluate the risks and benefits of hormone sparing sterilization methods. Additionally, most veterinarians and animal welfare groups indicate that it is critical to spay or neuter your cat. Some even recommend that they be spayed by four months of age to avoid pregnancy.

Hormone-sparing sterilization for cats as shown by a Bengal cat sleeping on a bed.

So why is there more research on spay and neuter in dogs than for cats? We think that the lack of research in cats and the consistent emphasis on spay/neuter is likely due to two factors. The first is the cat overpopulation problem. Additionally, there is a perceived incompatibility of an intact cat’s natural behavior with our expectation of “ideal pet behavior”.

Here is some information about health impacts of spay and neuter. Weight gain is the most commonly discussed outcome from spay/neuter. Obesity or overweight after spay or neuter can affect as many as 63% of cats.  This can lead to serious health issues like diabetes, constipation, orthopedic disease, urinary tract disease, and liver disease. Some types of cancer may be higher in neutered cats than for intact cats. However, the data are complex and more research is needed. 

Pros and cons of hormone-sparing sterilization in cats

The rationale for spaying and neutering your cat is not trivial. Cats can become pregnant as early as four months of age and males are sexually mature at 7-9 months. Cats can have kittens three or more times per year if they have access to males. So, sterilization is certainly important. But could hormone-sparing sterilization be accomplished with vasectomy or hysterectomy (as in dogs)? The simple answer is yes. Technically a cat could have a hysterectomy or vasectomy to ensure that no kittens will be produced.

A recent publication described another procedure called an epididymectomy for cats. This procedure involves removal of part of the epididymis where sperm mature and are stored. The epididymectomy makes it impossible for sperm to move to the vas deferens during ejaculation, causing infertility. Scientists found that it was a simpler procedure than castration without influencing hormones. You can read a summary of the study here and its potential application to feral cat populations.

However, there are other reasons cited for early spay and neuter of cats. One is that by removing the sex organs, there is no concern for diseases of those organs (testicular or ovarian diseases). Likely a more influential reason is that cats with natural sex hormones will exhibit behaviors that most people find difficult for a house pet. This includes yowling when seeking a mate, urine spraying, roaming to find a mate, and fighting with other cats. Spay or neuter surgery has been used to reduce hormone-driven behaviors, but neutering does not stop all cats from urine spraying.

Finding a veterinarian to perform a vasectomy or hysterectomy on a cat could be a challenge. If hormone-sparing sterilization of your cat is of interest to you, check with your local vet or one from our Veterinary Directory.

For more information and instruction on hysterectomy, vasectomy, and nonsurgical methods:

Benefits to shelters and veterinarians

Now that we understand the potential negative health impacts of spay and neuter, why don’t all veterinarians and shelters offer hormone-sparing options? Veterinarians are not yet routinely trained to perform these alternative sterilization procedures. Shelters may worry that changing the current standard of spay/neuter may confuse potential pet adopters or that dogs with natural hormones will be more difficult for pet owners, leading to more dogs at the shelter. Even though these concerns are not supported by research, it takes time for new procedures to be adopted.

The Parsemus Foundation encourages a consideration of all options and an individualized decision-making process regarding sterilization, as is recommended by the American College of Theriogenologists. Shelters offering hormone-sparing sterilization options will have an answer for potential adoptees who would otherwise be turned off from shelter adoption because of mandatory traditional gonadectomy. Veterinarians offering the option are already in great demand.

Other considerations: Identification and Therapy


It is important to be able to identify a dog that has had a hormone-sparing sterilization to prevent unneeded repeat surgeries if the dog is rehomed or lost. Be sure to discuss identifying your dog that is scheduled to receive a vasectomy or hysterectomy with your veterinarian. Learn more here:

Hormone therapy

Is your dog suffering from health or behavior problems ? Have you exhausted all other veterinary treatments with no luck? Was your dog spayed or neutered at a young age? Consider that your dog’s symptoms might be related to loss of hormones from spay or neuter. Hormone restoration therapy to normalize hormone levels for spayed or neutered dogs is in its infancy, but is an area of growing interest. See our page on Canine Hormone Restoration for more information and resources.

Take Action on Hormone-Sparing Sterilization

For Veterinarians

  • Veterinarians who wish to be listed in the directory may do so by filling out the info on the clinic registration form.
  • Use this flyer as an informational piece for your website or as a handout for clients.
  • Email us at info@parsemusfoundation.org if you would like to consult with a veterinarian who is experienced with hormone-sparing sterilization.
  • Review the Additional Resources below. Take note of the  information about gonadectomy risks for specific breeds and mixed-breed dogs published by Hart and colleagues (2020) and stay abreast of recent updates in this rapidly evolving area of research.

For Pet Owners

  • Review this flyer to understand whether hormone-sparing sterilization is right for you and your dog. Keep in mind that impacts of spay/neuter vary by breed, size and other factors. Check the recent publications about cancer and joint disorders by dog breed and mixed-breed size.
  • Consult with a veterinarian who is familiar with the health issues related to spay/neuter and familiar with hormone-sparing options. Each dog and family is different, and having an expert consultation on the best method of sterilizing your dog is important. 
  • To find a provider you can search the Veterinary Directory or check the information at the Ovary Sparing Spay and Vasectomy Info Facebook Group. If you cannot find a provider nearby, you could pass along the information on this website to your own veterinarian and ask if he or she can provide the procedure. Email us at info@parsemusfoundation.org if additional assistance/advice is required.
  • Please let us know if you find a veterinarian who offers OSS or vasectomy and would like to join our directory!
  • If you choose to preserve your dog’s hormones, consider joining this Facebook group: Training and behavioral advice for Intact Dogs.

Veterinarians Offering Alternative Methods of Contraception

For Pet Owners

Looking for a veterinarian willing to perform procedures beyond surgical spay or neuter? Browse our directory of qualified veterinary professionals.

For Veterinarians

Do you offer alternative methods of contraception like ovary-sparing spay and vasectomy? Join our referral directory so new clients can find you.

Summary documents

  • Download our flyer for a brief overview of hormone-sparing sterilization.
  • Download our infographic on the risks of spay-neuter.

Media, interviews, books and websites

  • Check out this interview with Dr. Kutzler by Dr. Karen Becker of Healthy Pets
  • Should I Spay or Neuter My Dog? Understanding the Secret LIfe of Sex Hormones“. A booklet by Jane Messineo Lindquist that makes sex hormones easy to understand, and provides all the data on spay/neuter so you can make this important decision.
  • Healthy and Happy Dog by Dr. Suzanne Valente has a wealth of information on the problems associated with spay and neuter, as well as an alternative view regarding pyometra treatment and tubal ligation.
  • “Pukka’s Promise: The Quest for Longer-Lived Dogs”, A thought-provoking book by Ted Karasote with a chapter on spay-neuter and health.
  • In 2019, the New York Times published an essay by Dr. Alexandra Horowitz, a cognitive scientist who studies dogs, in which she argued that spaying and neutering puppies shouldn’t be standard policy — and isn’t automatically the “responsible” choice either.
  • In this 2019 article in the Washington Post, Karin Brulliard writes about how research is causing some owners and veterinarians to question the long-held tenet that fixing puppies — or fixing, period — is a necessary part of responsible pet ownership.
  • An August 2021 Washington Post piece by Alexandra Ellerbeck discusses the evidence that spay and neuter is no longer an automatic option for dogs.
  • For a well-researched and thoughtful review of ovary sparing spay from a pet owner’s perspective: Jessica Rhea “The Pros and Cons of Ovary Sparing Spay (OSS) for Your Dachshund” 2019.

Publications on health impacts of gonadectomy

Browse these publication resources

Hysterectomy and vasectomy training materials

Browse these training resources

Epididymal sterilization references

Browse these references

Identification of dogs receiving vasectomy and hysterectomy

Read these identification references

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