Project Summary: How Spaying and Neutering Affect 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. This page provides an overview of the research on the health effects of spay or neuter. 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.
Use our Veterinarian Directory to find a veterinarian near you who offers hormone-sparing sterilization.
NEW: Infographic on the risks of spay and neuter, which you can use to raise awareness.
Health problems after hormone loss in dogs
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.
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. The following table summarizes our current knowledge of potential positive and negative health impacts.
Summary of health impacts of spaying and neutering (gonadectomy):
|Lower chance of:||But higher chance of:|
|Diseases of the sex organs: ||
How does spaying and neutering impact health?
A significant contributor to the negative health impacts of removing the hormone-producing sex organs in dogs is that the natural feedback mechanisms become unregulated. Normally, the hypothalamus and pituitary glands in the brain stimulate the production of luteinizing hormone (LH). The LH surge then stimulates the production of steroid hormones (like estrogen or testosterone) from the gonads. Without the ovaries or testes, there is no feedback signal to the brain to reduce production, so LH continues to be produced and may be the reason for diverse health problems. A study by Zwida and Kutzler in 2016 reported on the health implications of high LH levels in dogs without gonads. A review article on the ailments associated with spay and neuter — and the connection with LH — was also published by Kutzler.
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).
Don’t hormones cause undesirable dog behavior?
Many people believe that neutered male dogs make better pets because they are less aggressive. However, research does not 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 (urine marking, mounting and roaming) but impacts on other behaviors are variable.
Take Action on How Spaying and Neutering Affect Health
- 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 email@example.com 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 brief 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 firstname.lastname@example.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.
- Download our flyer for a brief overview of hormone-sparing sterilization.
- Download our infographic on the risks of spay-neuter.
Select publications on health impacts of gonadectomy
- For a video overview of the topic: Michelle Kutzler 2021 Presentations at AMVAC Conference.
- Belfield WO. 1972.For a more normal life for a pet: Partial spay (hysterectomy).Vet Med Small Anim Clin
67(11):1223-4. Full text. First publication covering why and how to conduct a partial spay on dogs.
- Brent L. 2019. Growing interest in hormone sparing dog sterilization and recommendations for standard identification methods. Clin Theriogenology 11(3):247-253. Full text.
- Brent L, Kutzler M. 2018. Alternatives to traditional spay and neuter – evolving best practices in dog sterilization. Innovative Vet Care. Free full text.
- de la Riva GT, Hart B, et al. 2013. Neutering dogs: Effects on joint disorders and cancers in Golden Retrievers. PLoS One. Free full text.
- Farhoody P, Mallawaarachchi I, et al. 2018. Aggression toward familiar people, strangers, and conspecifics in gonadectomized and intact dogs. Front Vet Sci 5:1-13. Free full text.
- Hart BL. 2001. Effect of gonadectomy on subsequent development of age-related cognitive impairment in dogs. J Am Vet Med Assoc 219:51-6. Abstract.
- Hart BL, Hart A, et al. 2014. Long-term health effects of neutering dogs: comparison of Labrador Retrievers with Golden Retrievers. PLoS One 9(7). Free full text.
- Hart BL, Hart A, et al., 2020. Assisting decision-making on age of neutering for 35 breeds of dogs: Associated joint disorders, cancers, and urinary incontinence. Front Vet Sci 07 July, 2020. Free full text. Supplementary data by breed.
- Hart BL, Hart A, et al., 2020. Assisting decision-making on age of neutering for mixed-breed dogs in five weight categories: Associated joint disorders and cancers. Front Vet Sci 31 July, 2020. Free full text. Supplementary data by weight.
- Kutzler M. 2020. Possible relationship between long-term adverse health effects of gonad-removing surgical sterilization and luteinizing hormone in dogs. Animals. Free full text.
- Lissner E. 2013. “The pros of partial spay. Innovative Vet Care. Full text.
- Mattravers M. 2017. Ovary sparing spay in canines: An alternative to traditional ovariohysterectomy. Full text. Student review.
- Society for Theriogenology, Board of Directors, and the American College of Theriogenology. 2013. Basis for Position on Mandatory Spay-Neuter in the Canine and Feline. Free full text. A good review of the data and recommendations from veterinarians who specialize in reproduction.
- Zink MC, Farhoody P, et al. 2014. Evaluation of the risk and age of onset of cancer and behavioral disorders in gonadectomized Vizslas. Abstract.
- Zink, MC. 2020. Canine gonadectomy: Rethinking long held beliefs. YouTube video.
- Zwida K, Kutzler M. 2016. 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. J Etiol Anim Health 1(1):1-11. Full text.
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.
Do you offer alternative methods of contraception like ovary-sparing spay and vasectomy? Join our referral directory so new clients can find you.
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