A New Option for Dog Neutering

Image via Shutterstockby Dr. Jennifer Coates, DVM | petMD.com


I like neutering dogs. Now don't get all Freudian on me, my reasons are medical in nature. It's a straightforward procedure, and unpleasant surprises are rare.

Contrary to what many owners (mostly men) think, the pain associated with the surgery is easily controlled with injections of local anesthetics into the spermatic cords and around the small skin incision, and ordinary pain relievers. When I'm given the opportunity to neuter a dog before problem behaviors (e.g., aggression, marking, mounting, etc.) arise, I am fairly confident that they never will, which goes a long way towards ensuring that a dog will remain a cherished family member.

But as with all things medical, neutering is not without its downsides. Certain diseases appear to be more prevalent in dogs who are neutered early in life, including prostatic cancer, weight gain, hip dysplasia, cruciate ligament rupture, and lymphosarcoma. Some owners (again, mostly men) are also resistant to neutering their dogs for what I can only guess are "there but for the grace of God go I" reasons.

In my opinion, for most owners and dogs the benefits of a surgical neuter outweigh its risks, but a new procedure that may be commercially available as early as next year could put a new option into the mix. It involves injecting each testicle with a small amount of a solution containing zinc gluconate. This is how it works, according to the manufacturer's website:

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After the injection, the Zeuterin™ solution diffuses in all directions from the center of the testis. The specific concentration of Zinc (a targeted spermicide) used in our formula destroys spermatozoa in all stages of maturation in the seminiferous tubules and in the epididymis. The seminiferous tubules, which were replete with spermatozoa, are now emptied and collapse.

The dog's body increases blood flow and creates inflammation to heal. Within days, scar tissue (or fibrosis) from the healing process creates blockages in the seminiferous tubules, and more importantly, in the rete testis (the part of the testis that feeds the epididymis). All sperm must finally pass through these feeder tubules, which are now effectively closed as a result of the specific location of the injection. Zinc Gluconate and Arginine are absorbed and metabolized by the body. The male dog is now safely sterilized for life...

The injection does not eliminate the cells that are responsible for producing hormones like testosterone. The manufacturer reports:

Mean serum testosterone levels were 41 to 52% lower in the groups treated with Zeuterin™ compared to the control group throughout the dose determination study. However, there were dogs in all treated groups that had testosterone levels similar to those for the control dogs at Months 1, 3, 6, and 9, and from 12 to 24 months post-injection. By Month 24, the testosterone levels for all but nine of treated dogs were in the same range as control dogs.

I am not an "early adopter." I am concerned that these higher testosterone levels might lead to an increase in problem behaviors like aggression and/or the diseases that we rarely or never diagnose in surgically neutered dogs (e.g., prostatic hyperplasia, prostate infections, and testicular cancer). Also, previous incarnations of this product resulted in an unacceptable incidence of adverse reactions (generally intense inflammation of the testicles or scrotum). The manufacturer says the five hour training that is required of veterinarians this time around will minimize those risks, but that remains to be seen. I will, however, be watching with interest to see what happens if and when this new procedure is tried on a greater number of client-owned dogs.


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