Hormone-sparing Male Sterilization

Methods for preserving hormones in male pets

Health impacts of neutering

In 2007 a respected veterinarian published a review of the pros and cons of spaying and neutering at different ages (Determining the optimal age for gonadectomy of dogs and cats, Margaret Root Kustritz.) This has generated substantial discussion and some further research, and thought leaders are beginning to accept that spay and neuter have both positive and negative health consequences that vary by age, gender, and breed, and that we’re only beginning to understand the situation.

In particular, mounting evidence indicates that in at least large dogs, the health benefits of keeping the hormones may outweigh the health risks. A recent publication from U.C. Davis (de la Riva, Hart et al, 2013) looked at two joint disorders and three cancers– hip dysplasia, cranial cruciate ligament tear, lymphosarcoma, hemangiosarcoma and mast cell tumor– and showed that, for all five diseases analyzed, the disease rates were significantly higher in both males and females that were neutered either early or late compared with intact (non-neutered) dogs. For males, the health pro and cons tip even more strongly in favor of keeping the hormones than in females, since the only health conditions prevented by neuter are benign prostatic hyperplasia in older dogs (which is treatable by neuter or PEMF), and testicular cancer (which is also a disease of old age and treated by castration, which is usually curative).

For an overview of health issues related to removal of the testes and ovaries and review of contraceptive options, see this article in the Innovative Veterinary Care journal written by Drs. Linda Brent and Michelle Kutzler.


Hormone-sparing sterilization

Surgical neuter (or the nonsurgical alternative, calcium chloride) will always have a place in spay/neuter, because it reduces the hormone-driven behaviors (roaming, mounting, fighting, marking) that make it hard to keep intact male dogs in homes. However, as a result of the health data, a set of highly-motivated and informed potential adopters is beginning to question or resist the mandatory neuters required to adopt from a shelter. In particular, those thinking of adopting breeds known to have greater risk of certain problems after neuter may be in this category (for example, Rottweilers and giant breeds are prone to bone cancers). But this is a highly distressing development to shelters, which fear going backwards on the progress on euthanasia rates and overpopulation that has been made thanks to widespread spay/neuter.

In these situations, veterinarians should be prepared to give adopters and owners a choice. As long as sterilization is achieved, clients should be free to request either a hormone-sparing sterilization procedure, or a behavior-changing neuter procedure such as surgical neuter.

Shelters offering hormone-preserving options will have an answer for potential adoptees who would otherwise be turned off from shelter adoption because of mandatory traditional neuter; and veterinarians offering vasectomy and other hormone-preserving options are likely to be in great demand.

More information

We maintain a list of veterinarians open to performing vasectomy or other hormone-sparing sterilization options for male dogs. Please contact us if you are a veterinarian who wishes to be included on this list. If you’re a dog owner/guardian and have a veterinarian who might like to offer vasectomy or another hormone-sparing technique, please consider passing the information along. And please let us know if you have any experience to share, whether especially positive or negative, with contacting one of these vets!

– More about hormones and health: Pukka’s Promise by Ted Kerasote, author of Merle’s Door
– More links to the science on hormones and health: Parsemus Foundation Ovary-sparing spay page for female dogs


Specific methods


Although it is not widely performed, vasectomy is an accepted way to sterilize dogs without impacting hormones. A number of veterinarians are willing to offer vasectomy (for example, for clients who want to sterilize their dogs right away to prevent accidental litters, but wait for neuter until after the dogs’ growth plates close). We are gathering a list of veterinarians who offer vasectomy. If you choose vasectomy for your dog, be sure to ask the vet to look into current recommendations for human vasectomy techniques, as some techniques have been shown to be more effective than others (such as cautery with fascial interposition) and are now considered best practice.

Resources: American Urological Association Vasectomy Guidelines (published 2012; amended 2015).


Please note that as of early 2016, Zeuterin is no longer available

Zeuterin is an “in between” sterilization method: in between testosterone-preserving vasectomy and testosterone-eliminating castration. It is thought to reduce testosterone on average 41-52%, and not to change behavior much. Conveniently, it is an injection rather than surgery. In addition, it is FDA-approved, produced by Ark Sciences, and should be easier to find than a vet offering vasectomy. Conceptually, it is an interesting option for those seeking a “middle path” (who are okay with partial hormone reduction). However, there are many anecdotal reports in circulation of post-injection pain or abscess, and subsequent histology that reveals some remaining spermatogenesis. 

Vanderstichel et al. (2015) Recent publication reporting variable testosterone levels in dogs chemically castrated with Esterilsol (Zeuterin). Abstract

Epididymal injection of calcium chloride

Calcium chloride in alcohol testicular injection is becoming better known as a faster, lower-cost, less traumatic alternative to neuter surgery. It is usually used as a one-time intratesticular injection that results in significant decreases in testosterone and permanent sterilization (see our calcium chloride page for more info). But based on studies in other species and in studies of other sterilants in dogs, we think when injected into the epididymis, the sperm storage area, instead of the testicles, it could have potential as a hormone-preserving option and a nonsurgical alternative to vasectomy in both humans and animals.

Immature sperm leave the testes and travel to the epididymis where they mature and are stored till needed. Injection of calcium chloride into the epididymis can stop sperm from being produced but not affect the production of testosterone, which is made in the Leydig cells of the testes. Epididymal injection of calcium chloride has been tried in bulls, and epididymal injection of another substance (chlorhexidine) has been studied in dogs (see below). A recent study using calcium chloride in alcohol in dogs has confirmed that sterility can be achieved while preserving testosterone.

With informed consent, a veterinarian could offer epididymal injection of calcium chloride to an owner seeking hormone-preserving sterilization but not wanting to subject the dog to vasectomy surgery (calcium chloride in alcohol rather than chlorhexidine is likely a more cautious place to start from a safety standpoint). A sperm sample would determine whether the injection had been successful or not. If you are a veterinarian who, after careful research, provides calcium chloride epididymal injection to a well-informed owner specifically requesting it, you can further science for the benefit of all dogs by sharing your experience with us at info@parsemus.org

2012 overview of epididymal injection approach and references
Blockage of Sperm Transport Using Intraepididymal Calcium Chloride Injections in Rams: Bowman et al., 1978. Free full text.
Epididymal injection papers using chlorhexidine injection by MH Pineda: 1977 dogs (Am J Vet Res); 1978 dogs (Canine Pract);1981 dogs (Theriogenology), and 1984 cats (Am J Vet Res)
Epididymal injection of chlorhexidine in dogs: Aiudi, Silvestre, Leoci et al, ACC&D 4th International Symposium, 2010, abstract and poster
Effects of intratesticular vs intraepididymal calcium chloride sterilant on testicular morphology and fertility in dogs. Leoci et al.  2019. Theriogenology. Free full text.

Epididymal injection of sotradecol

Sotradecol is an inexpensive drug commonly used as a sclerosant to collapse spider veins in humans. (Polidocanol, a newer and more expensive drug used for the same purpose, is reported by some doctors to not work as well or smoothly.) Sotradecol can be injected into varicose veins in liquid or foaming form. 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 (not running as much into the testicles or vas deferens). Safety is likely, given the extensive use in humans for spider veins over many years. Like with other epididymal injections, a sperm sample would determine whether the injection had been successful or not.

Please contact us if you are a veterinarian or researcher who accumulates data on this approach that you wish to share. A small publication prize is available for publication of IACUC-approved research in a peer-reviewed open-access journal.

Overview of epididymal sotradecol injection approach

Epididymal ligation

This is an interesting, extremely simple, low-cost technique that has been published in rams. It might not work in dogs because of anatomical differences in epididymal size and position, but could be tried.


Tamadon A. 2010. Epididymis ligation: a minimally invasive technique for preparation of teaser rams. Free full text. Also, earlier conference presentation: Tamadon et al. 2009. Pinhole epididymis ligation: A novel technique for teaser rams preparation. Free download.
Gur et al. 2011. The effects of prepubertal epididymal ligation upon androgen receptor distribution in the rat caput epididymis. Free full text.


Ultrasound is a non-invasive treatment using equipment already common in physical therapists’ offices. It has proven difficult to get it to work in animals with larger testes to confirm reports of efficacy in humans and primates in the 1970’s, but it has been effective in recent publications in rats and mid-size dogs. Researcher Raffaella Leoci is the primary investigator publishing on the use in dogs in modern times; her team’s 2009 publication can be found online, and the 2015 publication details the exact methods necessary for effectiveness in mid-size dogs (permanent sterilization is not achieved if the settings are not right).


Leoci et al. 2009. Ultrasound as a mechanical method of male dog contraception. Abstract
Leoci et al. 2015. Therapeutic Ultrasound as a Potential Male Dog Contraceptive: Determination of the Most Effective Application Protocol. Free full text.


Vasalgel is a contraceptive that is currently being developed for humans (see our Vasalgel page), but the concept is applicable to dogs and other species. Vasalgel works by injecting a polymer gel into the vas deferens – the tubes that carry the sperm – which blocks the sperm but allows fluids to pass through. The procedure does not affect hormones and is reversible. Further research is planned on the applicability of Vasalgel for dogs and cats.