Project Summary: Hormone-Sparing Sterilization Procedures
Hormone-sparing sterilization procedures — 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. This page includes details of the procedures to inform dog owners and provide educational resources for veterinarians.
Use our Veterinarian Directory to find a veterinarian near you who offers hormone-sparing sterilization.
Infographic on the risks of spay and neuter, which you can use to raise awareness.
Project Topics
What are the options for hormone-sparing sterilization in dogs?
All veterinarians in the U.S. are trained to complete spay and neuter surgery, which removes the gonads (ovaries in females and testes in males) and makes the pet sterile.
- Spay (ovariohysterectomy): abdominal surgery to remove the ovaries, uterus and cervix. Sometimes just the ovaries are removed (ovariectomy).
- Neuter (orchietcomy): a simpler procedure in which the testes are removed.
Very few veterinary schools train new practitioners on hormone-sparing sterilization procedures. Because the Parsemus Foundation routinely receives requests from veterinarians – and curious pet owners – about the procedures, we have included details here. We are also happy to connect veterinarians with questions to those more experienced with the procedures. Just send us a message at info@parsemus.org.
How is hysterectomy or ovary-sparing spay performed in dogs?
The most common hormone-sparing sterilization procedure for female dogs is a hysterectomy, or removal of the uterus and cervix while leaving the ovaries. It is sometimes called ovary-sparing spay (OSS) or partial spay. The procedure is not new: Belfield published on the need for the technique in 1972. OSS removes the nuisance of bleeding during heats, along with the risk of infection of the uterus (pyometra), as long as ALL of the uterus is removed. If some uterine tissue is left, “stump pyometra” may occur. More details of the technique are included in this publication and see Additional Resources for videos and other training information. (Note: the reason that tubal ligation is not usually offered to dogs is that pyometra can still occur).
The female dog will still have hormones, and may behave differently during the heat cycle. And while she cannot get pregnant, she may be attractive to males during heat — so owners may want to keep her indoors or away from intact males during this time.
What about health concerns of keeping the ovaries? Ovarian cancer is rare enough in dogs that the ovaries should not be removed just to try to prevent it. That makes mammary tumors the remaining concern. Although early studies reported a higher incidence of mammary tumors in intact dogs, a review article indicated that most of these studies were biased, making conclusions suspect (Beauvais et al., 2012). In one study, mammary tumors were reported in 1.25% of older female dogs, with higher incidence in poodles, English cocker spaniels, and dachshunds (Zatloukal et al., 2005). Luckily, mammary tumors are pretty easy to detect when rubbing your dog’s belly, and prognosis for the tumors that become cancerous is good when they are caught early and removed. Thus, many believe the low health risk associated with natural hormones is preferable to the more serious potential health risks of traditional spay. Ovary-sparing spay is approved by the American Veterinary Medical Association.
See “Additional Resources” below for details and training materials on OSS.
How is vasectomy performed in dogs?
Vasectomy in dogs is similar to the procedure for men. Each vas deferens (a tube that carries sperm from the testes and epididymis to the urethra during ejaculation) is cut or clamped so that sperm cannot move through. The procedure is completed under anesthesia but is relatively quick and simple. Technical details can be found here. This method of sterilization is accepted by the American Veterinary Medical Association.
There are few health concerns when completing a hormone-sparing sterilization on a male dog, since the only health conditions prevented by neuter are benign prostatic hyperplasia in older dogs (which is treatable by neuter or noninvasive electromagnetic therapy), and testicular cancer (which is also a disease of old age and is treated by castration, which is usually curative).
The dog will be sterile but will still have hormones and be attracted to females in heat. Thus, owners must be willing to keep their dogs from roaming in search of females.
Other hormone-sparing sterilization procedures for male dogs
Epididymal sterilization
Immature sperm leave the testes and travel to the epididymis, where they mature and are stored until needed. Methods aimed at the epididymis, rather than the testes, have the advantage of stopping sperm while preserving natural hormones (which are made in the Leydig cells of the testes). Several epididymal sterilization studies show promise for this as a hormone-preserving sterilization method.
Calcium chloride dihydrate solution is an effective chemosterilant that is normally injected into the testes to cause sterility and a significant drop in testosterone. But when injected into the epididymis, calcium chloride provides a nonsurgical hormone-preserving option for male dogs (see our Calcium Chloride Male Sterilization page). A recent study by Leoci and colleagues confirms that sterility can be achieved with an intra-epididymal injection of calcium chloride in dogs, with no drop in serum testosterone. However, the procedure required ultrasound guidance and took as long as castration. Intra-epididymal use of calcium chloride may be best for dogs who cannot tolerate surgery or whose owners do not wish to have any change in behavior or anatomy.
Sotradecol is an inexpensive drug commonly used as a sclerosant to collapse spider veins in humans. Although it has not been tried, foaming sotradecol might be an optimal epididymal injection, sclerosing the epididymis and staying in place more than a liquid sterilant. This prior art description of epididymal sotradecol injection provides more information on the approach.
Another epididymal approach tested in rams is epididymal ligation. This is an interesting, extremely simple, low-cost technique. It might not work in dogs because of anatomical differences in epididymal size and position, but has not been tried to our knowledge.
Ultrasound
Ultrasound is a non-invasive sterilization treatment for males using equipment commonly available in medical offices. Raffaella Leoci is the primary investigator who published two studies in dogs; a 2009 publication can be found online, and the 2015 publication details the exact methods necessary for effectiveness in mid-size dogs. This method has not progressed because permanent sterilization depends on specific equipment settings.
Vasalgel
Vasalgel is a contraceptive that is currently being developed for humans (see our Vasalgel page), but the concept is also applicable to dogs and other species. Vasalgel works by injecting a polymer gel into the vas deferens — the tube that carries the sperm — which blocks the sperm but allows fluids to pass through. The procedure does not affect hormones and is being developed as a reversible option for men by NEXT Life Sciences.
Zeuterin/Esterisol
Please note that as of early 2016, Zeuterin is no longer available but was approved by the FDA.
Zeuterin/Esterisol was an intra-testicular injection of zinc gluconate neutralized by arginine that reduced — but did not eliminate — testosterone in male dogs.
Scientists are working on other nonsurgical sterilization methods for male and female dogs and cats. See the Alliance for Contraception in Cats and Dogs for more info.
Take Action on Hormone-Sparing Sterilization Procedures
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 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.
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.
Additional Resources
Summary documents
- Download our flyer for a brief overview of hormone-sparing sterilization.
- Download our infographic on the risks of spay-neuter.
Hysterectomy and vasectomy training materials
- Kutzler M. 2021 Alternatives in sterilization and contraception in dogs Presentation at AMVAC Conference.
- Kutzler M. 2020 Gonad-sparing surgical sterilization in dogs. Frontiers in Vet Sci. Good overview article with description of procedures and images of OSS surgery.
- Romagnoli S, Krekeler N, de Cramer K, et al. 2024. WSAVA guidelines for the control of reproduction in dogs and cats. J. Small An Prac May 28. Details and images of procedures.
- For an informative overview of ovary-sparing spay, view the Powerpoint lecture: Hysterectomy by Dr. Michelle Kutzler.
- Human vasectomy guidelines: American Urological Association Vasectomy Guidelines (published 2012; amended 2015).
Epididymal sterilization references
- Bowman TA, Senger PL, Koger LM et al. 1978. Blockage of Sperm Transport Using Intraepididymal Calcium Chloride Injections in Rams. J Anim Sci 46(4):1063-1065. Free full text.
- Gur FM, Timurkaan S, Timurkaan N. 2011. The effects of prepubertal epididymal ligation upon androgen receptor distribution in the rat caput epididymis. Veterinarni Medicina 56(6): 286–293. Free full text.
- Leoci R, Aiudi G, Cicerelli V, et al., 2019. Effects of intratesticular vs intraepididymal calcium chloride sterilant on testicular morphology and fertility in dogs. Theriogenology 127:153-160. Free full text.
- Pineda MH, Reimers TJ, Faulkner LC, et al. 1977. Azoospermia in dogs induced by injection of sclerosing agents into the caudae of the epididymides. Am J Vet Res 38(6):831-8. Abstract.
- Pineda MH, Hepler DI. 1981. Chemical vasectomy in dogs. Long-term study. Theriogenology 16(1):1-11. Abstract.
- Pineda MH, Dooley MP. 1984. Surgical and chemical vasectomy in the cat. Am J Vet Res 45(2):291-300. Abstract.
- Tamadon A, Nikahval B, Sepehrimanesh M et al. 2010. Epididymis ligation: a minimally invasive technique for preparation of teaser rams. Veterinary Surgery 39:121-127. Free full text
- Last updated on November 14, 2024
Tell us what you think
What People Are Saying
I am so thankful for this site. I have referred people to you for years. … I’ve told people about the option of hormone-sparing surgeries and also managing their intact animals with integrity and compassion. I look at your site and tell them about veterinarians near them who can do these surgeries.
Website Visitor
Laparoscopic ovariectomy in cats is safe, can be performed in a comparable amount of time as traditional ovariohysterectomy, and may result in less postoperative discomfort.
Case et al.
The societal practice in the U.S. of dog neutering contrasts with the general attitudes in many European countries, where neutering is commonly avoided and not generally promoted by animal health authorities.
Torres de la Riva, et al.
Based upon the review of the literature, it becomes clear that canine gonads are not merely reproductive organs but critical to endocrine, musculoskeletal, behavior, and antineoplastic health.
Zwida & Kutzler
Recent scientific studies demonstrate that spaying/neutering, particularly before a dog is fully mature, may result in detrimental long-term health impacts. In light of this information, AKC encourages breeders, owners and veterinarians to consult on the appropriateness and timing of spaying or neutering an individual dog.
AKC Position Statement on Spaying and Neutering
About the only positive effect on behavior that seems to result from spaying and neutering is the roughly 68 percent decrease in urine marking.
Stanley Coren Ph.D., F.R.S.C
Thought leaders are beginning to accept that spay and neuter have both positive and negative health consequences that vary by age, gender and breed.
Elaine Lissner
Pet Health News
Spreading the message about the importance of hormones to dogs
The Parsemus Foundation is an educational resource for the public and veterinarians about the importance of hormones for pets. Over the years, we have received increasing inquiries about hormone-sparing sterilization from pet parents, and seen more veterinarians offering vasectomy or hysterectomy. But the shift in practice has been slow — until now. With several influential veterinarians spreading the message about the importance of hormones to dogs, this topic has finally reached the mainstream.
Cognitive dysfunction syndrome in cats similar to Alzheimer’s disease
House cats live an average of 14 years, and it’s not uncommon for a cat to live more than 20 years. Older cats often develop cognitive decline resulting in dementia. It’s called “cognitive dysfunction syndrome” or CDS. This condition is similar in many ways to Alzheimer’s disease, including amyloid beta and tau protein accumulation. Some believe that environmental stressors from life as a house cat contribute to cognitive decline.
Noninvasive methods to evaluate canine BPH
Most intact male dogs will develop enlarged prostate glands. This condition, known as benign prostatic hyperplasia (BPH), is influenced by androgen hormones such as testosterone. BPH has few symptoms in the earlier stages of development. However, it can lead to serious health issues if left untreated, such as reproductive tract issues, constipation, and prostate infections. Researchers have outlined noninvasive methods to evaluate canine BPH in the early, subclinical, stages. Early detection allows early treatment and avoids the progression of the disease.
Spreading the message about the importance of hormones to dogs
The Parsemus Foundation is an educational resource for the public and veterinarians about the importance of hormones for pets. Over the years, we have received increasing inquiries about hormone-sparing sterilization from pet parents, and seen more veterinarians offering vasectomy or hysterectomy. But the shift in practice has been slow — until now. With several influential veterinarians spreading the message about the importance of hormones to dogs, this topic has finally reached the mainstream.
Cognitive dysfunction syndrome in cats similar to Alzheimer’s disease
House cats live an average of 14 years, and it’s not uncommon for a cat to live more than 20 years. Older cats often develop cognitive decline resulting in dementia. It’s called “cognitive dysfunction syndrome” or CDS. This condition is similar in many ways to Alzheimer’s disease, including amyloid beta and tau protein accumulation. Some believe that environmental stressors from life as a house cat contribute to cognitive decline.
Noninvasive methods to evaluate canine BPH
Most intact male dogs will develop enlarged prostate glands. This condition, known as benign prostatic hyperplasia (BPH), is influenced by androgen hormones such as testosterone. BPH has few symptoms in the earlier stages of development. However, it can lead to serious health issues if left untreated, such as reproductive tract issues, constipation, and prostate infections. Researchers have outlined noninvasive methods to evaluate canine BPH in the early, subclinical, stages. Early detection allows early treatment and avoids the progression of the disease.
Additional support for delaying spay/neuter in large-breed dogs
When it comes to spaying or neutering your dog, the timing of the procedure can significantly impact their long-term health. Traditionally, veterinarians have recommended spaying or neutering before six months of age. However, recent studies, including an update to the comprehensive studies by Drs. Benjamin and Lynette Hart from the University of California, Davis, have added to growing evidence that delaying these procedures can reduce the risk of cancer and joint disorders in certain breeds. Pet owners should also consider hormone-sparing sterilization as an alternative to traditional spay/neuter.
