Hormone-Sparing Sterilization Procedures

Female-dog-reproductive-system-Callouts for Hormone-Sparing Sterilization Procedures

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 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 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.


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.

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.

Hysterectomy and vasectomy training materials

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

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