PROJECT

Hormone-Sparing
Sterilization Procedures

PET HEALTH
PROJECT

Hormone-Sparing
Sterilization Procedures

PET HEALTH

Project summary

Spaying or neutering sterilizes a pet by removing reproductive organs — the testes in males and ovaries in females. The removed organs no longer produce hormones such as testosterone and estrogen. This hormonal imbalance may create health problems, such as cancer and joint disorders. More people are opting for hormone-sparing sterilization for their dog. This page provides details on the procedures.
Use our Veterinarian Directory to find a veterinarian who may assist you with hormone restoration.

Background

  • Hormone-sparing sterilization procedures, also called gonad-sparing sterilization, are ways sterilize dogs while leaving their natural hormones intact.
  • For females, hysterectomy surgery that removes the uterus but leaves the ovaries intact, is most commonly practiced. It is also called ovary-sparing spay.
  • For males, vasectomy surgery is performed in which the vas deferens (the tube that carries sperm) is cut or blocked so that sperm cannot flow.
  • Not all veterinarians offer hysterectomy and vasectomy yet, but the number is growing.

Key points

  • Hormone-sparing sterilization procedures usually include hysterectomy and vasectomy. Tubal ligation is not usually recommended because pyometra is still a concern.
  • Not all veterinarians offer hysterectomy and vasectomy yet, but the number is growing.
  • Other procedures, including nonsurgical or noninvasive methods, are being developed as well.
  • Our Veterinary Directory can help you find a veterinarian to perform these procedures.

Parsemus' role

  • The Parsemus Foundation serves as a hub to provide information to both pet owners and veterinarians on the procedures related to hormone-sparing sterilization.
  • Our website and Vetarinary Directory are maintained with up-to-date information and we are always available to answer questions.
  • Veterinarians seeking information on performing hysterectomy and vasectomy can find videos and details of the procedures here, and we are happy to assist in setting up consultation or training with experienced veterinarians.
The Project in Detail

Topics

  1. What are the options for hormone-sparing sterilization in dogs?
  2. How is hysterectomy or ovary-sparing spay performed in dogs?
  3. What about tubal ligation to sterilize female dogs?
  4. How is vasectomy performed in dogs?
  5. Other hormone-sparing sterilization procedures for male dogs
  6. Take action on hormone-sparing sterilization procedures
  7. Veterinarians offering alternative methods of contraception
  8. Additional resources
  9. Frequently asked questions

Female dog reproductive anatomy

Hormone-Sparing Sterilization Procedures

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’ve included details here. We’re 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’s sometimes called ovary-sparing spay (OSS) or partial spay. The procedure isn’t 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).

Management of a female dog with a hysterectomy

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.

What about tubal ligation
to sterilize female dogs?

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.

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.

Managing a male dog with a vasectomy

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, but the concept is also applicable to dogs and other species. It’s a polymer gel that’s injected 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. It’s being developed as a reversible contraceptive option for men by NEXT Life Sciences.

Zeuterin/Esterisol

This was an intra-testicular injection of zinc gluconate neutralized by arginine that reduced — but did not eliminate — testosterone in male dogs (*Please note that Zeuterin was approved by the FDA, but has not been available since early 2016.).

Take Action on
Hormone Sparing Sterilization 

For Veterinarians

  • Veterinarians who wish to be listed in our Veterinarian Directory should fill out our clinic registration form.
  • Use this flyer as an informational piece for your website or as a handout for clients.
  • Email us at  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 Veterinarian 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  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.

Veterinarian
Directory

Search for a Veterinarian

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.

Add your clinic to our Vet Directory

Additional resources

Summary infographics

Click image to view a larger version.

Hysterectomy and vasectomy training materials

Scientific publications

See our searchable bibliography for a complete library of scientific publications on our projects.

Key publications on epididymal sterilization:

  • 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

Frequently Asked Questions:
hormone-sparing sterilization

How Spay/Neuter Affects Health

Q: Why is “traditional” spaying and neutering being questioned now?

A: For decades, removing the gonads (ovaries/testes) was the standard for population control. However, research shows that these organs do more than just reproduce; they produce hormones (estrogen, progesterone, and testosterone) that are essential for development, bone density, muscle mass, and immune function. Removing them—especially in young dogs—can increase the risk of hip dysplasia, cruciate ligament tears, obesity, urinary incontinence, diabetes, and certain cancers like osteosarcoma or hemangiosarcoma.

Q: What are the pros and cons of traditional spay/neuter?

A: Deciding to remove a dog’s reproductive organs is a trade-off. It effectively sterilizes the dog, but while it eliminates certain risks, it increases others.

  • Pros (Benefits of removal): Eliminates the risk of diseases of the ovaries and testicles and those influenced by sex hormones. This includes pyometra, uterine/ovarian cancer, mammary tumors, and testicular cancer.
  • Cons (Risks of hormone loss): Increases the risk of several serious “non-reproductive” diseases. These include orthopedic issues (CCL tears, hip dysplasia), certain aggressive cancers (hemangiosarcoma, osteosarcoma, mast cell tumors), and metabolic or urinary issues (obesity, urinary incontinence in females).

Q: Which diseases become more common after a dog is spayed or neutered?

A: Research indicates that when a dog is deprived of sex hormones during development or throughout adulthood, the following conditions are more frequently observed:

  • Joint Disorders: Hip dysplasia and cranial cruciate ligament (CCL) tears (often due to the “delayed closure” of growth plates, leading to longer, weaker limbs).
  • Cancers: Lymphoma, Hemangiosarcoma (cancer of the blood vessels), and Osteosarcoma (bone cancer).
  • Behavioral/Other: Increased anxiety, noise phobias, obesity, and urinary incontinence.

Q: Why are some health problems more common in spayed and neutered dogs?

A: Without the sex hormones produced by the ovaries and testicles, the entire system becomes unbalanced. Normally, the hypothalamus and pituitary glands in the brain stimulate the production of luteinizing hormone (LH) and follicle stimulating hormone (FSH). The LH surge then stimulates the production of steroid hormones (like estrogen, progesterone 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 over-produced. Diverse health problems likely result from the loss of sex hormones and the high LH levels.

Q: Is the only alternative to keep my dog “intact”?

A: No. Many owners worry that the only way to keep their dog healthy is to leave them fully intact, which carries the risk of accidental litters. Hormone-sparing sterilization (such as vasectomy or ovary-sparing spay/hysterectomy) offers a “middle ground.” These procedures make the dog 100% sterile (unable to reproduce) while allowing them to keep their natural hormones and the health protections they provide.

Q: Is there a “best age” to spay or neuter?

A: There is no single “correct” age for all dogs. The ideal timing depends heavily on the dog’s breed, sex, and lifestyle. For example, a Great Dane may need to remain intact longer to allow their joints to fully develop, whereas a small breed may have fewer risks associated with early sterilization. This is why an individualized approach is essential.

Q: Does my dog’s breed affect when (or if) they should be neutered?

A: Yes, significantly. A landmark study of 35 different breeds showed that the “safe” age for sterilization varies wildly. For some breeds, neutering before one year of age significantly increases cancer and joint risks, while for others, the impact is minimal. Owners should consult breed-specific data before making a decision.

Q: How should I talk to my vet about this?

A: It is important to seek veterinary guidance from a professional who stays current on the latest research. You might ask: “Given my dog’s breed and health history, what are the specific risks of a traditional spay/neuter?” or “Are you familiar with hormone-sparing options like an Ovary-Sparing Spay or Vasectomy?” If your regular vet is not comfortable with these procedures, you can use the Parsemus Veterinary Directory to find a specialist who is.

Q: If I choose to spay or neuter my dog, does my dog’s age matter?

A: This study indicated the longer the dog had natural hormones, the more improved their health and behavior were. This applied to dogs that were left intact longer, dogs that had an ovary-sparing spay, and dogs that had a vasectomy.

Hormone-Sparing Procedures

Q: What is a Vasectomy for dogs?

A: Similar to the procedure in humans, a canine vasectomy cuts or blocks the vas deferens – the tube that carries sperm from the testicles out of the body. This makes the dog sterile (unable to reproduce) but allows him to keep his testicles and his natural testosterone. He will still be interested in “intact” females, but he cannot father puppies.

Q: What is an Ovary-Sparing Spay (OSS) or Hysterectomy?

A: In an OSS, the surgeon removes the uterus and part of the cervix but leaves one or both ovaries intact. This prevents pregnancy and eliminates the risk of “pyometra” (a life-threatening uterine infection), but the dog continues to produce the hormones necessary for healthy aging.

Q: Will a dog with an Ovary-Sparing Spay still go into “heat”?

A: Yes. Because the ovaries remain, the dog will still experience hormonal cycles. She may attract males and exhibit some behavioral changes associated with heat, but because the uterus is gone, she will not have a bloody discharge and cannot become pregnant.

Q: Will my dog’s behavior change after a hormone-sparing sterilization?

A: Hysterectomy or vasectomy will not change your dog’s behavior like traditional spaying and neutering. Because the dogs retain natural hormones, females will have a “dry” heat cycle and males may be interested in females in heat (although they cannot reproduce).

Q: Are these procedures harder to find?

A: Yes. Most veterinary schools still only teach the traditional spay/neuter procedure. However, the Parsemus Foundation maintains a searchable directory of veterinarians who are trained and willing to perform hormone-sparing procedures.

Q: Is a hormone-sparing spay more expensive?

A: It can be. Because it is a specialized procedure that requires more precision (to ensure all uterine tissue is removed while keeping ovaries safe), it may cost more than a high-volume, traditional spay. However, many owners view it as an investment in preventing future health costs and suffering.

Q: Where can I get ovary-sparing spay for my cat?

A: Ovary-sparing spay in cats is uncommon due to limited research on health impacts of gonadectomy in cats and intolerance towards behaviors associated with cat hormones (spraying, fighting, howling in heat). However, many veterinarians in our Veterinary Directory provide ovary-sparing spay in at least dogs so feel free to contact those veterinarians and inquire about ovary-sparing spay for your cat.

Q: Where can I get ovary-sparing spay for my dog?

A: The Parsemus Foundation’s Veterinary Directory lists specialists worldwide that can provide ovary-sparing spay procedures. In addition, you can discuss ovary-sparing spay with your regular veterinarian and share our page on Hormone-Sparing Sterilization Procedures with them. If you don’t find a veterinarian in your area, you may be able to find one by visiting the Ovary Sparing Spay and Vasectomy Info group on Facebook.

Identification of Sterilized Dogs

Q: Why is identification so important for these dogs?

A: If a dog with a hormone-sparing procedure ends up in a shelter, a vet might assume they are completely intact and perform a second, unnecessary surgery. Clear identification prevents “re-spaying” or “re-neutering” and ensures the dog’s unique hormonal status is understood by future medical providers.

Q: How can a vet tell if my dog was sterilized if they still have their gonads?

A: This is a major concern for owners of dogs with vasectomies or ovary-sparing spays. To an outside observer or a shelter, these dogs look “intact.” The Parsemus Foundation advocates for clear identification methods, such as a standardized tattoo on the abdomen (a small green “X” for hysterectomy or “V” for vasectomy). Adding specific notes in the dog’s microchip record will also be useful.

Last updated on September 10, 2026

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What people  are saying

“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

“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.

“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.

“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.”

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