Neutering: Not Just Doggie Birth Control

dog at vetDexter, a new dachshund patient of mine, was in last week for another round of puppy shots. He will soon be six months old and it was time for me to discuss the next step in his preventive health care plan: neutering.

Neutering meets the guidelines
The American Veterinary Medical Association has developed guidelines for responsible pet ownership. One of the guidelines obligates pet owners to control their pet’s reproduction through spaying and neutering; subsequently helping to control pet overpopulation in their community. Neutering is the common term for castration of a male dog or cat and spaying refers to removal of the ovaries and uterus, or in some cases just the uterus or ovaries, of a female pet.

Lifesaving responsibility
Pet overpopulation is a serious issue in the United States today. According to the Humane Society of the United States, over four million unwanted pets are destroyed annually. For every puppy or kitten prevented by neutering an adult pet, there is one less homeless and unwanted puppy or kitten euthanized in an animal shelter.

The traditional surgery
Surgical removal of the testicles is the current standard of care for neutering in both dogs and cats. This surgery renders a male dog or cat unable to reproduce and also removes the major source of the male hormone, testosterone. Removing the source of testosterone eliminates mating behavior in males and also plays a role in eliminating other unwanted behaviors. In both the dog and cat, neutering involves a small skin incision through which the testicles are removed. Cats typically go home the same day, but dogs may stay overnight to recover from anesthesia and for incisional monitoring.

A new method
The New York Times Well Blog recently reported on a new method of non-surgical, chemical castration, called Zeuterin. Zeuterin neutering uses zinc gluconate and arginine injected into a dog’s testicles as a less invasive method of castration. Dogs still produce a small amount of testosterone, but are unable to sire a litter of puppies. Veterinarians must be trained to use the Zeuterin method of neutering, but especially for shelters and rescue groups, the method has great appeal.

My recommendation
Dexter’s owners were concerned about the surgery. They asked if he could just have a vasectomy instead of the traditional neutering surgery. Because my job is to make the best medical recommendations for the specific health concerns of each of one my patients, I recommended the traditional surgery for Dexter. It provides him with the greatest number of health benefits. The surgery prevents unwanted litters of puppies and also prevents prostatic disease, testosterone-induced tumors and behaviors linked to testosterone production. Because a vasectomy or Zeuterin neutering are methods of birth control only, they do not offer the added advantage of decreased levels of testosterone on behavior and disease.

7 Responses to Neutering: Not Just Doggie Birth Control

  1. James Serpell says:

    Dr. Weedon is broadly-speaking correct about the effects of castration on behavior in dogs. Most studies show quite marked effects of castration on urine marking, escaping/roaming, sexual mounting, and inter-male aggression in male dogs but little in the way of significant benefits in relation to stranger-directed or owner-directed aggression or aggression directed toward other dogs in the same household. Indeed, we have some evidence that these and several other behavior problems may be made worse (e.g. fear/anxiety, excitability). The real problem is that existing studies are inconclusive due to various design flaws. The definitive case/control study with before and after assessments of behavior and testosterone levels has never been attempted. Until somebody does this, the jury is still out in my opinion.

  2. G. Robert Weedon, DVM, MPH says:

    While I recognize that prostatitis, benign prostatic hypertrophy, and prostatic abscess are testosterone responsive diseases, no one has determined at what cut point the reduction of testosterone has to be to effectively manage these conditions. Does it have to be reduced by 99%? Perhaps. But if a 50% reduction has a protective effect, then we prevent these conditions, and preserve some normal function of the hormone. What about prostatic adenocarcinoma? The incidence is higher in castrated males. Will preserving some of the testosterone function protect against that? Dunno. Certainly worth looking into.
    Respecting the issue of testosterone-driven behavior, I agree that sterilization decrease roaming, urine marking, and mounting behaviors in male dogs. I’m not so sure about the aggression. My friend, and colleague, Dr. James Serpell, at the University of Pennsylvania has some pretty compelling data that shows that inter-dog aggression, fear aggression, touch sensitivity are all more commonly seen in sterilized males and females. I will copy him on this post so that he might weigh in on the discussion. I think we need to be very careful about how we frame the behavior effects of neutering. If some testosterone-driven behaviors are decreased with castration, the question still remains; can they be decreased with the testosterone reduction that is seen with Zeuterin? That remains to be seen, and will require a lot more work to determine the cause and effect.

    G. Robert Weedon, DVM, MPH

  3. Dr. Weedon,

    Thank you for reading Fur the Love of Pets and for taking the time to comment on my most recent blog. You and Dr. Kay both raise an interesting point on the possibility of positive effects of long term low levels of testosterone in male dogs and I hope some creative researcher will pursue this avenue of study to end speculation on this topic.

    Prostatitis, benign prostatic hypertrophy and prostatic abscess are testosterone responsive diseases and according to the 7th edition of Ettinger and Feldman’s Textbook of Veterinary Internal Medicine are treated in part, by neutering. My colleagues who are experts in management of behavior disorders in dogs recommend neutering to decrease roaming, urine marking, aggression and mounting behaviors in male dogs. J Am Vet Med Assoc 1991;198:1204-5.

  4. Dear Dr. Kay,

    Thank you for reading Fur the Love of Pets and for taking the time to comment on my most recent blog post. You raise an interesting point on the possibility of positive effects of long-term low levels of testosterone in male dogs, and I hope some creative researcher will pursue this avenue of study.

    As a member of both the Oncology and Small Animal Internal Medicine Colleges, I am aware of the research on canine prostate cancer. But my interpretation of the studies differs a bit from yours and influenced my writing. There is clearly mounting retrospective evidence of an association between spay/neuter status and cancer in pet dogs. As an author of one such study which shows an association between spay/neuter and the occurrence of canine mast cell tumors, I also understand the limitations of the currently available data. These studies suffer from confounding and/or selection bias questions such as: Are neutered dogs more likely to receive specialty care than unneutered dogs? Thus, is the population of dogs studied at university teaching hospitals and specialty centers and reported in the literature biased towards neutered dogs and would a study of a more representative population of dogs give a different result with regard to the question on prostate cancer and neutering?

    Retrospective studies provide low levels of evidence to support causality and those such as the canine prostate cancer studies support an association, but not neutering as the cause of prostate cancer. Given the wide variety of cancers that have been associated with spay/neuter, I believe some will ultimately be more strongly associated with the absence of sex hormones than others. Even the results of prospective observational studies are influenced by uncontrolled confounding. Only adequately powered randomized controlled prospective studies can answer questions regarding the influence of spay/neuter on cancer in our canine companions.

    We have an epidemic of unwanted pets in the U.S. today and thankfully not an epidemic of prostate cancer in dogs. I feel strongly about the need to encourage neutering to decrease the number of unwanted pets euthanized in our shelters.

    I remember you from our days at Cornell. I believe you were two classes ahead of me and I couldn’t wait to have the white jacket and stethoscope like you! Congratulations on the success of Speaking for Spot and I hope you continue to read Fur the Love of Pets.

  5. G. Robert Weedon, DVM, MPH says:

    I’m curious as to what the benefits “of decreased levels of testosterone on behavior and disease,” exactly are? What evidence is there that eliminating testosterone is healthy? Zeuterin has been shown to reduce circulating testosterone by half. Perhaps reducing it by half, rather than eliminating it, would actually be healthier for the dog?

  6. Dr. Nancy Kay says:

    Hi Dr. Hohenhaus,

    I read your comments about Zeuterin with great interest. I think that Zeuterin is an intriguing neutering option in that, as you mentioned, it reduces rather than eliminates the animal’s production of testosterone. There has been some recent compelling evidence in Rottweilers and Golden Retrievers suggesting that elimination of testosterone may be associated with increased incidence of cancer and shortened life expectancy. It is possible, though not yet researched, that “half-strength” testosterone (which Zeuterin accomplishes) may end up being the best bet in terms of inducing sterility along with enhancing longevity. Clearly there is a great deal more research to be done in terms of spaying and neutering our companion pets.

    I would like to offer one correction to the information you have posted. Surgical neutering does not eliminate the incidence of all prostate gland diseases. Prostate gland cancer (the most severe type of prostate gland disease) occurs more commonly in neutered compared to nonneutered dogs.

    Best wishes for the holidays!

    Dr. Nancy Kay
    Diplomate, American College of Veterinary Internal Medicine

  7. Mark Wilde says:

    More and more individuals are fascinated in taking care of animals and so, as a responsible pet lover, they must consider pet neutering. It can be the single best decision to make for long-term welfare. However, it is necessary to have a trusted and reliable vet to perform this particular method.

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