To Spay or Not To Spay?
There are many advantages of spaying for dog parents and society - but (traditional) spaying likely negatively impacts the quality and length of her life.
Animal shelters around the country are filled with unwanted puppies and dogs. The American Society for the Prevention of Cruelty to Animals (ASPCA) reports that approximately 6.5 million animals enter the shelter or rescue system annually. Of those 6.5 million animals, only an estimated 3.2 million find their way out of the shelter or rescue and into a home.
This quote comes from the PET MD website page on Spaying and Neutering Dogs and is the reason that spaying and neutering is so important - in general. But let’s be honest, many pet owners have 100% control over the reproductive activity of their dogs and they have no difficulty keeping their female dogs away from potential suitors while they are in heat.
For many of these pet parents the choice to spay is really about not having to deal with the bloody discharges, which vary by breed and are typically 2 to 4 weeks duration every 6 months.
But increasingly over time, our pets are being treated like our children. And just like our children, we will do just about anything to make sure they live full, happy and long lives. Hopefully, few would even consider sterilizing their teenage daughters to avoid monthly bouts of drama and irritability, so then it's natural for many pet parents to wonder if spaying harms the length and quality of their dog’s life.
National veterinary and pet advocacy groups have long claimed that spaying and neutering dogs improves dog health and longevity. Most frequently these groups cite the Hoffman et al 2013 paper, which analyzed the death records of over 80,000 dogs. The plot below shows the fraction of sterilized male and female dogs (blue lines) surviving to certain age ranges compared with unsterilized dogs (red lines).
It appears from these plots that sterilized dogs live longer. The authors conclude:
”Sterilization increased life expectancy by 13.8% in males and 26.3% in females among the {full cohort of} dogs.”
However, this conclusion is WRONG as we will see shortly.
As we’ve documented numerous times in previous Pure Science articles on Climate Change research and Covid-19 policies, scientific truths frequently lose the battle when they conflict with the narrative of a desired policy outcome - in this case, the well intentioned desire to prevent the death and imprisonment of hundreds of thousands of unwanted dogs per year via ubiquitous sterilization.
The simple truth is that spaying (and neutering of male dogs) is harmful to both the health and longevity of the dogs.
The magnitude of the effects are breed specific. The harmful effects of spaying and neutering are particularly noticeable in Golden Retrievers, which are prone to getting cancer. Thus, this issue is particularly important for Solo Saber (shown above), who shares a house with my oldest daughter and her fiancé and is an American Kennel Club pedigreed purebred Golden Retriever.
The highly cited Hoffman paper demonstrates the fundamental problem with all retrospective studies: ensuring that all the groups being compared are similar with regard to confounding variables. In the Hoffman paper, the comparison groups, sterilized and unsterilized dogs, clearly have large differences in confounding variables.
The big red flag in the Hoffman paper is that unsterilized dogs die from traumatic injuries and preventable/treatable infectious diseases at three times the rate of the sterilized dogs. Approximately 45% of the unsterilized dogs die due to these two causes of death - a fact left unstated by the authors but which can be inferred from other data available in the paper. Neither cause of death is likely related to sterilization status.
The authors speculate that the higher trauma rate of unsterilized dogs is due to a greater tendency to roam and more aggressive behavior. This argument could possibly be made for male dogs, who have been known to travel miles following the scent of a potential girlfriend in heat, but is far less likely with female dogs. However, the data in the Hoffman paper shows that both male and female unsterilized dogs are equally more likely (by a factor of 3!) to die from trauma than sterilized dogs of the same sex. A much more likely (and the only plausible scenario) is that owners who make the choice to NOT sterilize their dogs also are much more likely to let them roam freely, which exposes them to many dangers, primarily motor vehicles!
If we focus on dog causes of death that are likely related to sterilization status, we reach the opposite conclusion of Hoffman : Sterilization increases the two primary age-related causes of death, neoplasm (cancerous growths) and immune-mediated (diabetes, lupus, Crohn’s, etc.) by factors of 2.7 and 3.5, respectively.
Neutering does not just negatively impact lifespan. There is a reason that women who undergo hysterectomies are usually given hormone therapy. Hormones are essential components to overall health.
In a 2014 paper, Hart et al, show the negative effects of sterilizing Golden Retrievers and Labrador Retrievers include not just much higher cancer rates but also much higher incidences of joint disorders, including hip dysplasia and cranial cruciate ligament tear as shown below. Goldens sterilized while <6 months (still recommended on some terrible websites) get serious joint disorders around a quarter of the time!
The paper shows that delaying spaying and neutering reduces the negative effects on the dog joints, but for Golden Retrievers, even delaying spaying until the dog is at least 2 years old, still results in an almost doubling of the risk for the two most common joint disorders, which occur in approximately 5% of unsterilized dogs.
Options for current and prospective puppy parents
An option for female puppy owners is a ovary-sparing hysterectomy, where the uterus and part of the fallopian tubes are removed. This makes her unable to reproduce, but her ovaries remain and will produce beneficial hormones. She will still go in heat but the discharges should be greatly reduced. This surgery is more complicated and expensive than a traditional spay surgery and there is a chance of a serious complication called stump pyometra, which is why it is wise to seek out a vet that has extensive experience with this procedure.
For those planning to get a puppy, think about a mixed breed - the more mutt the better. Greater genetic diversity leads to better health for a wide variety of species. Data clearly shows small dogs live healthier and longer lives than big dogs for reasons unknown. It’s possible the enhanced expression of growth promoting genes in large breeds also promotes cancer growth. Finally, consider getting a male dog of a mixture of the least aggressive breeds (Golden Retrievers, Labradors Retrievers, Bernese Mountain Dogs, Brittany Spaniels, Greyhounds and Whippets) and let him keep his “doghood”. Counter to prevailing wisdom, it is not clear sterilization reduces aggression (neutering can increase biting and other bad behaviors in some breeds), which traditionally has been a primary reason put forth to neuter males dogs.
This is truly remarkable and I wish every Veterinarian would take a few minutes to read this!