A Nonsurgical Way to Neuter Male Dogs

Photo © Susannah Kay

There is some exciting news on the battlefront against pet overpopulation. A medication is hitting the U.S. market that is used to neuter male dogs without the need for anesthesia or surgery.

Used for the past few years in Mexico, Colombia, Bolivia, and Panama under the name Esterilsol™, Zeuterin™ (gotta love this name) is expected to be available in the United States within the year. Current FDA approval is for use in dogs between three and ten months of age although expansion of approval to all dogs over three months is anticipated soon.

The active ingredient in Zeuterin™  is zinc gluconate, which is the reason use of this product is referred to as “zinc neutering.” Within 30 days of administration, Zeuterin™ induces sterility. Only one treatment is needed and no significant hospital stay is required.

How it Works

Zeuterin™  is administered via injection directly into each testicle, without the need for anesthesia (mild sedation is frequently used). Now, before you cross your legs and mutter, “Yowza!” the manufacturer reports that 97.5% of dogs studied showed no outward evidence of pain during the procedure. Apparently, the combination of using a very small needle and slow injection of the product avoids triggering any sensation of discomfort. Post-procedure complications such as pain and injection site reactions occurred in only 1.1% of treated dogs.

Within 30 days of administration, Zeuterin™ induces sterility by causing permanent, irreversible scarring of the dog’s testicles. While the testicles eventually diminish in size, they do remain visible. Because of this, dogs neutered with Zeuterin™ are marked with a small tattoo in the groin area so that they can readily be identified as having been sterilized.

The Pros and Cons

For people who are in favor of sterilization, but cannot fathom the thought of their dog living without testicles, Zeuterin™ may be just the solution. On the other hand, if the primary goal of neutering is elimination of negative male behaviors such as roaming and aggression, surgery may still be the procedure of choice. Zeuterin™ does not completely eliminate testosterone production within the testicles. (Testosterone is a major driving force of negative male behaviors in some dogs.)

Zeuterin™ may be a real boon for animal shelters and spay/neuter clinics in the fight against pet overpopulation. Proponents believe chemical neutering is safer, simpler, less time consuming, and less expensive than traditional surgery. This means that more dogs can be neutered with available resources.

Are you curious to see how chemical castration is performed? If so, have a look at this video. Fear not, there is no pain or blood observed!

Is chemical castration likely to replace traditional surgical neutering in our population of pet dogs? I have no clear prediction, but I will certainly be interested to see how the answer to this question unfolds.

Would you consider chemical rather than surgical castration for your male dog?

Best wishes,

Nancy Kay, DVM

Diplomate, American College of Veterinary Internal Medicine
Author of Speaking for Spot: Be the Advocate Your Dog Needs to Live a Happy, Healthy, Longer Life
Author of Your Dog’s Best Health: A Dozen Reasonable Things to Expect From Your Vet
Recipient, Leo K. Bustad Companion Animal Veterinarian of the Year Award
Recipient, American Animal Hospital Association Animal Welfare and Humane Ethics Award
Recipient, Dog Writers Association of America Award for Best Blog
Recipient, Eukanuba Canine Health Award
Recipient, AKC Club Publication Excellence Award
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Please visit http://www.speakingforspot.com to read excerpts from Speaking for Spot and Your Dog’s Best Health.   There you will also find “Advocacy Aids”- helpful health forms you can download and use for your own dog, and a collection of published articles on advocating for your pet’s health. Speaking for Spot and Your Dog’s Best Health are available at www.speakingforspot.com, Amazon.com, local bookstores, and your favorite online book seller.



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13 Comments on “A Nonsurgical Way to Neuter Male Dogs

  1. Of course the manufacturer will say it is safe but in order for caretakers to decide, there needs to not only be independent studies, but also unbiased reporting by the veterinary community. Also instead of injecting more chemicals another alternative is a vasectomy.
    Here is an excellent article on the pros and cons of this procedure, including pictures

    Dr. Karen Becker has an excellent unbiased and informative report on this issue:
    http://healthypets.mercola.com/sites/healthypets/archive/2012/08/15/new-dog-sterilization-technique.aspx From the report:
    Zeuterin Adverse Reactions
    The 2003 FDA drug approval document includes a study of 270 male puppies injected with the chemical sterilant. The puppies were a combination of shelter animals and family pets.
    The following reactions were noted:
    Reactions Upon Injection Local Reactions
    Reaction Dogs Affected Reaction Dogs Affected
    Vocalization 6 Scrotal Pain 17
    Kicking 1 Scrotal Irritation 3
    Although the complication rate was similar for surgical and zinc-gluconate castration, the zinc-gluconate reactions were more severe. Surgical wound complications were treated by superficial wound debridement and resuturing. In contrast, zinc-gluconate reactions required antimicrobial treatment, orchiectomy, and extensive surgical debridement and reconstruction, including scrotal ablation in 2 dogs. These reactions occurred following administration by both experienced and novice individuals. All dogs made a full recovery following treatment of zinc-gluconate reactions and incisional dehiscences.

    • There is a higher risk of complications as compared to surgical castration. Some dogs will get extreme swelling of the testicles or scrotal ulcers afterwards and many of these dogs require surgery in order to remove the entire scrotum. I read of several cases of shelter vets who had used this method of castration and ended up euthanizing dogs who had severe reactions.
    • It takes a few months to weeks for the testicles to completely shrink.
    • Dogs who have had neutersol injection do not have as low testosterone levels as surgically neutered dogs. Because of this we don’t know if chemical castration will have the same benefits in reducing prostate problems and other testosterone related issues later on in life.
    • One study showed that many dogs who had chemical castration were later on neutered surgically because they had too many “male” behaviors such as mounting and peeing on things.

    Laura J. Sanborn, M.S. in her scholarly study, “Long-Term Health Risks and Benefits Associated with Spay / Neuter in Dogs” Animal Sciences Rutgers University (May 14, 2007) states: “no compelling case can be made for neutering most male dogs, especially immature male dogs, in order to prevent future health problems.”
    • The injection can be painful. (However, if proper sedation is given this is reduced. Some vets have reported that dogs actually tolerate the injections. well.www.naiaonline.org/pdfs

    From Dr. Marie Haynes of Ask a Vet a Question who has actually used this product:

  2. Thanks for raising this issue. I would have to say I would never chemically castrate my animals because we don’t know the long-term effects and because we all need fewer chemicals in our lives. I think it’s time that we all revisit the ‘pet overpopulation’ and ‘early spay/neuter’ issues as linked in any way other than long-term misguided ways of dealing with what someone thinks is ‘too many’ animals. There can be ‘too many’ of all things, but the science has been out for a long time that seriously questions early spay/neuter, and points out that it doesn’t work and it causes many illnesses, from obesity to thyroidism to cancer, and in fact can increase aggression.

    This would be a great time to explore this topic in more detail, include the research that argues against the practice of early spay/neuter, and begin to re-educate people on what it means. We are not reducing pet population: we are subjecting our animal families to debilitating illnesses and conditions that can ruin their quality of life and then kill them.

    Since I lost my beloved Cavalier in March to a cancer linked to early spay/neuter I’ve calmly told people about this issue, pointing to science and rationality, and they all say: ‘but we’re supposed to do it because we have too many animals.’ Sad. Horrifying. Most of us are responsible pet guardians. The rest are problem.

  3. This is not new news. Neutersol was approved in 2003, and this is just that under a different label. It may catch on this time around in the ever more gonad-phobic public mindset, but I kind of doubt it. I think Neutersol was on the market for five years, and I do not personally know of even one single dog for whom it was used.

    My dogs get to keep their bits unless there is either a medical or behavioral reason why de-sexing would be of benefit to them. I regard supervision and management to be perfectly effective means of birth control. So, no… I will not be considering this.

    I do prefer to keep intact animals. At this point, I am unlikely to acquire a shelter or rescue dog for this reason. If this becomes an option and if it becomes recognized as meeting the de-sexing criteria for competing with unregistered dogs in dog sports, then I could possibly consider a dog from a rescue or shelter. Not that a shelter or rescue would sell a dog to someone who doesn’t vaccinate adult dogs except for rabies, who lets the cat go outside, who feeds raw and doesn’t mindlessly speuter LOL!

  4. I would not consider castration under any circumstances short of its necessity for saving the life of my dog.

    I also hope Dr. Grudzien doesn’t write as badly as she types. Is it so very hard to type a long word like ‘be’ or ‘to’?

  5. Some of you have asked about long term consequences. I know of no long term studies (5-10 years out) with this product. No doubt time will tell. Within the last few days, I received a broadcast email from the drug manufacturer inviting me as a veterinarian to learn how to use this drug.

    Dr. Nancy

  6. It sounds promising but what do we know about long term side effects of injecting yet another chemical into our animals? There is already controversy about rabies and the “routine” vaccination protocol; if my male dog were not already surgically sterilized, I would still opt for the surgery, not knowing what effect the zinc might have (cancer?) down the road.

  7. Wow, cool!

    Right away I thought of a training evaluation that came in recently. Their dogs behavior issues weren’t necessarily related to being in-tact, but I asked them why he was not neutered, at 5 years old. The wife said the husband would not do it, and he admitted he wanted the dog to be able to experience sex. Yes, there are people out there who are really that stupid. I told him, as a breeder, I can tell you the male does not “enjoy” sex, and I have seen the stud in pain, as the penis is pulled backwards as they’re tied, and even vomiting afterwards. I told him not to breed the dog, and detailed several more reasons why. Still, he would not “do that to him.” Ugh. He would be perfect candidate for this.

    But it would also be perfect for many show breeders, protection sport competitors, k9s (the testosterone is wanted), and those who want their dog in-tact but not breed-able. People who want the dog in its natural state, and believe it is healthier for the dog, but want population control for the lifetime of the dog, no matter where it goes.

    I think this sounds fantastic. Two questions though: I would have a feeling of reservation about what other side effects there could be. Secondly, I wonder how this is different versus just a vasectomy? I am guessing it’s cheaper and faster?

  8. I have mixed feelings. On the one hand, I’m thrilled there’s a non-surgical option that may encourage more people to have their dogs neutered. On the other hand, I’m concerned that the “male behaviors” are not decreased. I mean, that was one of our arguments to folks FOR neutering, and if we take that away, will we discourage even MORE people from having their male dogs desexed?

  9. I absolutely will not overdose a dog’s testicles with zinc unless long-term, double-blind studies indicated its safety and confirm the least dose required for success without side-effects.

    I have had multiple intact males for three decades without a single unplanned pregnancy. Training and fencing completely control my male dogs without neutering.

  10. A couple of things here:

    1) I really don’t think altering male dogs has much effect on population. The number of puppies born is really dependent on females. If a female is spayed or protected while in season she won’t have unwanted puppies no matter how many intact males are running around. If she is unprotected she is likely to be bred even if most of the local males are neutered (or confined). For example, deer populations do not decline when hunting seasons are for bucks only. If you want to reduce the deer population there must be hunting seasons for does. In areas where populations of feral dogs are a problem, reducing the number of intact males is even less likely to reduce reproduction because it is unlikely you will be able to sterilize all the males in a population.

    2. Spaying and neutering is not a requirement for being a responsible dog owner, much as that has been drummed into the common psyche. There are valid reasons for not neutering dogs (either sex) that have nothing to do with reproduction. There is more and more evidence that it is healthier for dogs to remain intact, at least until physical maturity and probably longer, especially for males. Nor is it a panacea for behavioral problems and may cause as many as it solves. From a behavioral standpoint, neutering, for either sex, should be considered individually. This may actually be a plus on the side of chemical neutering, since it does leave at least partial testosterone production.

    3. I am concerned about this product getting into the hands of animal rights activists and rescue extremists. Though I am a responsible owner (and not a breeder) of well-behaved intact male dogs more than once I have been viciously, though verbally, attacked by extremists who think anyone who doesn’t spay/neuter is pretty much the scum of the earth. If all it takes to sterilize a male dog is a quick shot, I fear some will do this by stealth.

  11. Hi Jill,

    Thanks for your interest. The short term side effects have to do with inflammation/pain at the injection site, but such reactions appear to be few and far between (according to the manufacturer). I am unaware of any long term studies.

  12. Wow this sounds awesome, Nancy. Is there any information on the studies done for this procedure as in… how dogs were done over what period of time? Was there any follow up w/ dogs as they get into their senior years? Are there any risks for these drugs and if so, what are they? I will do my own research as well, just wondered what else you knew about this.

    Thanks again for keeping our world up to date w/ your continued pioneering work.

    aka Shewhisperer

  13. This sounds like the best thundering since sliced bread 2 me! I doubt that discomfort could b worse than surgery. I believe that it will b inferior 2 a surgical neuter due 2 continued testosterone production, bit this sounds like a great option for those who can’t afford surgery (no gen anesthesia, no bloodwork). I can’t wait 2 carry it!