Spay and neuter: a touchy subject
by Prescott Breeden

A meta-analysis on the pros and cons of spay and neuter in Dogs


The decision to spay or neuter a dog for owners is not as simple as figuring out what bag of treats to buy at the pet store.  It is a decision that will affect a dog for the rest of their life through changes in their health and their behavior.  Often the decision to spay or neuter is surrounded by feelings of guilt and moral acceptability.  With humans we find it morally reprehensible and condemn it, viewing it as an inhumane mutilation of the body and free will.  Dogs are being anthropomorphized more and more as can be observed by the growing number of pets acting as surrogate children for couples, thus the question of spaying or neutering a dog is sometimes met with an emotional reaction equivalent to the idea of castrating a child.  However, they are dogs, and as much as we love them with every ounce of our soul we have to make responsible decisions based on what we know scientifically and statistically so that our emotions are a reflection of intelligent decision making and not reactionary anthropomorphic ideology.

The positive and negative health and behavioral consequences of gonadectomy (spaying and neutering) have been being studied for over 50 years.  Hundreds of studies have been published and you could spend a year simply trying to read all the data.  However there was a recent study[i] published in 2007 that analyzed the data of 183 previous studies to determine the optimal age for gonadectomy (spay/neuter) in dogs and cats.  Twenty different health and behavioral conditions were reviewed and analyzed in the study.

In females, the results are shocking.   Tumors in the mammary glands (also known as Mammary gland neoplasms) have a 50.9% chance for malignancy.[ii]  Numerous studies have all concluded there is a correlation between dogs spayed after their first estrus cycle and their risk for developing mammary gland tumors.

“…dogs spayed before their first estrus have a 0.5% risk, dogs spayed after 1 estrus have an 8.0% risk, and dogs spayed after 2 estrus cycles have a 26% risk of developing mammary gland neoplasms when they get older”[iii]

But spaying late is still better than not spaying at all.

“…performing an ovariohysterectomy [spay] may even have a substantial sparing effect in older dogs, with a reduced but still evident reduction for mammary gland neoplasms in dogs spayed as late as 9 years of age.”[iv]

In addition to the health benefits, spaying or neutering can also help with behavioral issues such as roaming, a concern for both male and female dogs which can lead to unplanned litters, traffic accidents, and owner relinquishment to a shelter.  Roaming is a reproductive behavior that is caused by hormones and is described as having “adaptive significance” (an animal behavior that has an evolutionary benefit).  For example a dog that does not chew and strengthen her jaws will not be good at dissecting animal kills, thus rendering her malnourished and potentially preventing her from passing her genes down to the next generation.  Roaming is adaptively significant because dogs that do not roam are highly unlikely to find a mate drastically affecting the probability of procreation.  In a study of nearly 2,000 dogs that were relinquished to shelters for behavioral issues, escaping ranked third at 16.4%.[v]

The most major behavioral benefit of neutering is decreased aggression.  The neural circuitry that controls aggression is created during prenatal brain development with the presence of androgen (testosterone).  After that circuitry is set in place, it lays fairly dormant until the animal reaches puberty and the testes start producing significantly higher amounts of androgen.  When androgen hits receptors in the brain, the circuit is completed and aggressive behavior results.  By neutering a dog early, you remove the detonator from the bomb and the likelihood of aggressive behavior is significantly reduced.

Many dog owners do not realize that intact male dogs also display significantly more social dominance cues to other dogs.  These displays are often misinterpreted and result in defensive aggression from males who have been neutered (see related article: a response to my readers).  There’s no scientific way around it: in a social environment, intact males are the primary source of inter-species male aggression.

The behavioral benefits of spaying and neutering are only demonstrated when the procedure is done at an early age, not at the sign of a symptom.  Veterinarians frequently recommend neutering once aggressive tendencies have been observed, however these dogs have reached an age where the effects that a gonadectomy can have for potential behavior modification are significantly lowered.  For a dog to have the behavioral benefits of a gonadectomy, they must be spayed or neutered before puberty.  Since 50% to 70% of all dog euthanasia is the result of behavioral problems, it is crucial to understand that the decisions an owner makes for their dog with behavioral consequences affects the health and survival of that dog.[vi]

Perhaps the most depressing issue is that some veterinarians are advocating late spay or neuter for their clients.  I have a client who told me her vet recommended she wait two to three years before getting her Golden Retriever neutered, and another that told me his vet recommended to wait a year before neutering his Leonberger.  What many vets have jumped at is a study that found a correlation in increased incidences of hip dysplasia in dogs that were spayed and neutered before five months of age.[vii]  However, any veterinarian that has read the study should dismiss using it as a foundation for recommending the age for spay/neuter.  The problem is that while the study had a massive number of dogs (1,842), it is only one study and the findings were unclear whether a veterinarian confirmed the diagnosis of the hip dysplasia in all the afflicted dogs.  In addition to the weakness of this study, hip dysplasia is a hereditary condition that is predominantly affected by genetics, diet, and exercise.  In essence, regardless of the time of spaying and neutering, good husbandry is a crucial element to the prevention of hip dysplasia, both in breeding practice and caretaking.

Dr. Charles DeVinne, DVM, says, “The role I play is to discuss the benefits versus the risks with the procedure, give statistically reliable references, and let the owner make the decision.” He continues, “I usually recommend spaying and neutering at five months.  The health advantages in females and behavioral benefits in males have been observed, studied and well documented.  If your vet is recommending a late spay/neuter you should get a second opinion, perhaps from an experienced board certified oncologist, internal medicine specialist, behaviorist, or orthopedic surgeon.”

It is irresponsible for a dog owned by a non-licensed breeder to not be spayed or neutered.  On top of all the health and behavioral benefits from spaying or neutering, intact dogs are the primary reason that the shelter system in the United States is over flowing.  The unplanned litters and behavioral problems that lead to thousands of owner relinquishments and euthanasia can only be stopped if owners will spay and neuter their dogs.  Owners must not project their feelings onto their dogs about the human emotional reaction surrounding castration and ovariohysterectomy.  Many owners feel that it is ok for them to not fix their dogs because they are a “backyard-dog”.  This ideology stems from what B.F Skinner always referred to as “Autonomous Man Ideology”.  It’s behavior of a person knowing 600,000 people will die from heart related issues but will ignore their cholesterol, or a person knowing 50,000 people will die in car crashes over the holiday weekend but will still drive to grandma’s thinking they aren’t at risk, that it doesn’t apply to them.  Dogs escape and have social interactions, even if they are inhumanely chained to a post.

We live in an integrated and complex society and no single dog owner is exempt from the fact that within this society, every dog has an effect on the society as a whole.  Dog owners must be responsible for their dog’s health, their behavior, and the effect their dog has on the community.

References:

[i] Kustritz, M. V. R. (2007) Determining the optimal age for gonadectomy of dogs and cats, Journal of American Veterinary Medical Association, 231, 1665-1675.

[ii] Kustritz, M. V. R. (2007) Determining the optimal age for gonadectomy of dogs and cats, Journal of American Veterinary Medical Association, 231, 1665-1675.

[iii] Schneider, R., Dorn, C.R., Taylor, D. (1969) Factors influencing canine mammary cancer development and post-surgical survival.  Journal of the National Cancer Institute, 43, 1249-1261.

[iv] Verstejen, J., Onclin, K. (2003) Etiopathogeny, classification and prognosis of mammary tumors in the canine and feline species. Proceedings. Annu Conf Soc Theriogenol, 230-238.

[v] Salman, M. D., Hutchinson, J., Ruch-Gallie, R., Kogan, L., New, J. C., Kass, P. H., Scarlett, J. M. (2000) Behavioral Reasons for Relinquishment of Dogs and Cats to 12 Shelters, Jounral of Applied Animal Welfare Science, 3(2), 93-106.

[vi] Salman, M. D., Hutchinson, J., Ruch-Gallie, R., Kogan, L., New, J. C., Kass, P. H., Scarlett, J. M. (2000) Behavioral Reasons for Relinquishment of Dogs and Cats to 12 Shelters, Jounral of Applied Animal Welfare Science, 3(2), 93-106.

[vii] Spain, C. V., Scarlett J. M., Houpt K.A. (2004) Long-term risks and benefits of early-age gonadectomy in dogs.  Journal of American Veterinary Medical Association, 224, 380-387.