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 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. See Deeper Dive below.

While spay and neuter helps to reduce pet overpopulation, it comes at a price. Gonadectomy removes the ovaries and testicles, but these are the same organs that produce hormones important for development and health. Research over the last two decades has shown that 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.

Hormone-sparing sterilization offers a way to preserve natural hormones while ensuring that you pet cannot reproduce.

Brief history of spay and neuter

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.

Our understanding of the health impacts of spay and neuter started with research evaluating dogs that had their sex organs removed (called gonadectomy) at a very young age. In 2007, a respected veterinarian named Margaret Root Kustritz published a review of spaying and neutering dogs and cats at different ages. This generated a lot of discussion and further research reporting positive and negative health consequences of gonadectomy that vary by age, gender, and breed.

Today there is mounting evidence that the health benefits of keeping the sex organs in dogs may outweigh the health risks. A key 2013 publication from the University of California, Davis reported that the rates of two joint disorders and three cancers in Golden Retrievers were significantly higher in both males and females that were neutered early or late compared with intact (non-neutered) dogs. Many other studies have followed. For example, a 2014 study indicated that gonadectomized Vizslas had significantly increased odds of developing mast cell cancer, lymphoma, all other cancers, and fear of storms compared with the odds for sexually intact dogs. Brain tumors are also 11 times more likely in spayed than intact females. On the positive side, since dogs who have been spayed or neutered no longer have sex organs, they don’t get diseases associated with sex organs or hormones.

There is also evidence that it is the loss of hormones from spaying and neutering dogs that is causing an increased risk of long-term health problems. A study by Zink and colleagues reported that intact dogs and those sterilized with hormone-sparing procedures (vasectomy or hysterectomy) had reduced risk of general health problems and both problematic and nuisance behaviors as compared to spayed or neutered dogs.

Whether your dog might have health problems following spay or neuter depends on many factors, including the breed, sex, age of sterilization, and body size. Follow-up studies from the University of California, Davis have reported risk profiles of 35 breeds and mixed breed dogs, providing important information for veterinarians and pet-owners when considering sterilization.

If you are considering sterilization options for your dog, consult with an experienced veterinarian to discuss the risks and benefits for your dog. And be sure to consider hormone-sparing sterilization procedures in your assessment. The following table summarizes our current knowledge of potential positive and negative health impacts.

As a result of the health problems that occur more frequently after gonadectomy, pet owners and veterinarians have sought alternatives. That is where hormone-sparing sterilization comes in. Ovary-sparing spay (or hysterectomy) for females and vasectomy for males are surgical methods that sterilize the pet while preserving the organs (ovaries and testes) that produce natural hormones. These options are great for breeds known to have greater risk of certain problems after spay/neuter (for example, Boxers have a higher chance of brain tumors, Rottweilers and giant breeds are prone to bone cancers, and Golden Retrievers have higher chances of orthopedic conditions and cancer after hormone loss).

Many people believe that neutered male dogs make better pets than intact male dogs because they’re less aggressive. However, research doesn’t support this conclusion. A recent large survey reported that spayed or neutered dogs did not differ from intact dogs in terms of aggression directed toward familiar people or pets, and they actually showed higher levels of aggression toward strangers. Dog aggression is a main reason for relinquishment to shelters, and neutered male dogs are more often surrendered for behavioral reasons. Gonadectomized dogs may also develop more anxiety and fear, and show more cognitive decline than intact dogs.

Behavior is complex and related to the dog’s environment, rearing, and training. Neutering male dogs may decrease reproductive-related behaviors (such as urine marking, mounting, and roaming), but its impact on other behaviors is variable.

• 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.

• Review this flyer to understand whether hormone-sparing sterilization is right for you and your dog. Keep in mind that impacts vary on 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. Direct him or her to the information on this website and 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.
• Has your dog already been spayed or neutered? See information about hormone restoration for dogs.

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

Last updated on February 21, 2025