I’ve written extensively over the years about the risks and benefits of neutering. It’s a complicated subject that tends to draw a lot of passion even in the absence of robust scientific evidence. Variable such as sex, breed, age at neutering, and the particular procedure performed all influence the risk, and there are few conditions for which we can make absolute predictions in an individual dog or cat. The best we can say is that a few conditions are clearly much more common in intact animals (e.g. uterine infections, breast cancer), some are more common in neutered animals (e.g. obesity), and many, many conditions are influence subtly by neutering and also by many other variables.
The overall outcome for any individual is affected by so many factors that it is effectively unpredictable. Strident claims that neuteringmustbe done or should notbe done or that the age at which it is done is crucial conflict with the much more nuanced and complex reality evidence in the scientific research on the subject. A balanced, rational approach is to recognize that some risks increase and others decrease with neutering and that the best we can do is make tentative recommendations for individual pets based on the population literature. As the evidence changes, new research can shift our estimate of the risks and benefits, though radical revisions in practice are rarely justified. A new piece of evidence recently published strengthens one claim that has been tentatively made based on previous research; neutered dogs appear to live longer on average than intact dogs.
A number of studies in dogs (as well as other species, including humans) have found greater longevity in neutered animals than in those left intact.1-9Not all studies agree, and there are significant differences in longevity between breeds. There are also potential differences in other factors, such as the quality of husbandry and medical care received by intact versus neutered animals, especially in countries in which neutering is the norm. Generalizations about the effect of neutering on lifespan may not apply to every individual, but overall the pattern in the research literature has been for neutered animals to live longer than intact animals.
A recent retrospective study looking at records from a chain of hospitals across the U.S. evaluated lifespan in a cohort of over 2 million dogs seen at these clinics during a two-year period.
Silvan R. Urfer, Mansen Wang, Mingyin Yang, Elizabeth M. Lund, and Sandra L. Lefebvre (2019) Risk Factors Associated with Lifespan in Pet Dogs Evaluated in Primary Care Veterinary Hospitals. Journal of the American Animal Hospital Association: May/June 2019, Vol. 55, No. 3, pp. 130-137.
The results showed statistically significant differences in lifespan associated with neuter status and breed size. The figures below illustrate the key findings.
These data agree with the majority of the results of previous studies, which suggests that the relationship between neutering a longevity is real. This does not, of course, explain what this relationship is. Differences in breed, husbandry and medical care, specific causes of death, and many other factors are involved in determining lifespan. However, it is at least clear that broad claims neutering shortens lifespan are not consistent with the evidence.
This study also provides a good example of a problem common in the interpretation of scientific literature, which is the difference between statistical and real-world significance. It is possible to find differences between groups which are statistically significant, especially if you include a very large number of subjects, but these differences can be effectively meaningless in the real world. In this study, for example, the difference between the median lifespan of neutered and intact male dogs was 0.06 years (about three weeks). This is clearly not a meaningful difference in the life of an actual male dog.
The difference between spayed and intact females, in contrast, was 0.58 years (about 7 ½ months). This is a more significant difference in terms of real life, though still small as a portion of the overall lifetime of a dog.
Breed size had a much larger effect, with giant breed dogs (over 90 lbs adult weight) living almost four years less than small-breed dogs (under 20 lbs adult weight). This too is consistent with previous research though again it doesn’t explain the cause for this difference.
This study strengthens the claim that neutered dogs live longer than those that are not neutered. Longevity is affected by breed, sex, care, and many other factors, and the reason for this difference is unclear. The magnitude of the difference in lifespan between intact and neutered dogs varies among studies, and the difference is not always large enough to be of any real-world significance. However, these results clearly contradict broad claims about the overall negative effect of neutering on health and longevity in dogs.
- Michell AR. Longevity of British breeds of dog and its relationship with sex, size, cardiovascular variables, and disease. Veterinary Record 1999;145(22):625-9.
- Bronson RT. Variation in age at death of dogs of different sexes and breeds. American Journal of Veterinary Research 1982;43(11):2057-9.
- Moore GE, Burkman KD, Carter MN, Peterson MR. Causes of death or reasons for euthanasia in military working dogs: 927 cases (1993-1996). Journal of the American Veterinary Medical Association 2001;219(2):209-14.
- Drori D, Folman Y. Environmental effects on longevity in the male rat: exercise, mating, castration and restricted feeding. Experimental Gerontology 1976;11(1-2):25-32.
- Greer KA, Canterberry SC, Murphy KE. Statistical analysis regarding the effects of height and weight on life span of the domestic dog. Research in Veterinary Science 2007;82:208-14.
- Kraft W. Geriatrics in canine and feline internal medicine. European Journal of Medical Research 1998;3:3-41.
- Waters DJ, Shen S, Glickman LT. Life expectancy, antagonistic pleiotropy, and the testis of dogs and men.Prostate 2000;1:43(4);272-7.
- Hoffman JM, Creevy KE, Promislow DEL. Reproductive Capability Is Associated with Lifespan and Cause of Death in Companion Dogs. PLoS ONE. 2013;8(4): e61082. doi:10.1371/journal.pone.0061082
- Cooley DM, Beranek BC, Schlittler DL, Glickman NW, Glickman LT, Waters DJ. Endogenous gonadal hormone exposure and bone sarcoma risk. Cancer Epidemiology, Biomarkers, and Prevention 2002;11:1434-40.
Did the authors multiply the years by seven?
Kudos to your critical evaluation of the study. Someone who is biased towards neutering dogs might have just run with the conclusion “Neutered dogs live longer” without looking at the details. You clearly did better than that!
Thanks for the information. Good to know.
My dog was a pediatric neuter, I got him when he was almost a year old. He has had no health issues at all and is approaching his 7th birthday.
He is somewhat aggressive/prey driven, all male, behaviorally speaking.
There was a woman on another forum that would go on and on how her dog was not neutered and because of that, healthier and better than our neutered dogs.
They certainly had N large enough to get statistical significance after dividing the sample into sub groups. Any chance they did, or could look at early neutering? Specifically, it would be useful to have better evidence about :
1. The extent to which speying before the first season prevents reproductive system diseases (mammary cancer, pyometria, etc).
2. If there is harm, other than conformational changes that wouldn’t sit well in the show ring, in pediatric (say, before 4 months) neutering.
Even with large samples sizes, post-hoc subgroup comparisons are a it dodgy. It is very easy to run a million different comparisons and stumble across a statistical difference without actually having uncovered a biologically meaningful relationship. Ideally, prospective studies (e.g. cohort) with an a priori hypothesis that are designed to compare outcomes in dogs neutered at different ages would be stronger evidence.
In terms of the issues in #1, we do have some evidence here. Certainly, neutering prevents pyometra, that is quite clear. The specific impact of neutering at different ages on mammary cancer risk is less clear, though the bulk of the evidence suggests neutering is protective in general.
A couple of years ago, my male intact dog was going to surgery to remove a mass from the skin, and the vet asked me if I wanted to take the opportunity to neuter him, since he would be under general anesthesia. Based on your previous comprehensive collection of articles (http://skeptvet.com/Blog/wp-content/uploads/2014/12/Benefiits-Risks-of-Neutering-in-Dogs-and-Cats.pdf), I said no, because, as you state there in your conclusions, for male dogs without any behaviour or prostate issues, the risks of neutering seem to overcome the benefits.
Do you still have the same opinion after this new evidence?
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I still believe the evidence suggests little meaningful difference in the length and quality of life for most male dogs whether they are neutered or left intact. As you can see from this study, the difference in life-expectancy for males was about three weeks, and all the other factors that influence lifespan are likely to swamp such a small difference in the real world.
A number of studies in dogs (as well as other species, including humans) have found greater longevity in neutered animals than in those left intact.1-9>>>>>
From memory the only prospective randomized study addressing this question in humans showed a 2yr decrease not increase. Are all your references addressing your human claim behind paywalls?
here Is the article that made me ck out the prospective nurse study.
the rotti study in the article like all the other dog and cat ones that I have read about was not prospective. the nurse study I think was randomized. I remember being shocked that they would remove ovaries or not in nurses at a flip of a coin.
The data seems to come from dogs in the US where dogs are neutered by default unless you want to breed – did they take pregnancies into account? Or on the other hand the majority of the intact dogs hasn’t been cared for and has never been to the vet?
Yes, the data come from Banfield primary care veterinary hospitals in the U.S. However, the fact that the majority of dogs are neutered in the U.S. does not in itself affect the comparison of health outcomes in neutered and intact dogs. About 10% of the female dogs were intact and about 13% of the male dogs.
I don’t know what you mean by “:take pregnancies into account?” The study compared overall life expectancy, not mortality due to specific causes nor reproductive history, so I’m not sure what this has to do with interpreting the conclusions.
The study required dogs to have been seen at the vet at least twice during the two-year study period, so it is not true that intact dogs did not receive veterinary care. In fact, the frequency of visits was associated with shorter lifespan, implying more vet visits mean a less healthy individual.
Now, it is possible that one reason for the difference in survival was a difference in the level of medical care received (or a difference in any of a hundred other variables), but the study did not specifically look at that question. Dental cleanings appeared associated with longer survival,. which could be a direct effect or a proxy for more aggressive medical care, but it could also be a statistical fluke. Always hard to tell what is important and what happenstance in such “big data” studies.
Of course, the duty does not have to stand in isolation. There is other evidence that gonadectly increases lifespan in a variety of species, and some investigations of possible mechanisms, so this data are at least consistent with what we known from other research.
I see you have some research by Dr David Waters who I have known for years based on his 100 Year Rottweiler Club studying longevity in that breed. In that effort ongoing Dr Waters has found that at least among Rotties that spaying and neutering before six years of age definitely reduces their chances of reaching old age primarily because they become more likely to come down with osteosarcoma. In my own experience with six Rotties over 30 years three spayed females died before reaching ten. They also all had ACL surgeries which his data suggest is also related to spaying. Contrast this with our eight year old in tact female and she maintains a body more like a three year old and has never had ACL issues. And doesn’t suffer from weight issues.
Unfortunately, it is not as straightforward as that. Dr. Waters did report that duration of exposure to ovarian hormones increased the chances of achieving exceptional longevity in those dogs. However, a previous study of the same population reported intact females lived an average of 7.5 years, compared to 9.8 years for spayed females.(Cooley DM, Beranek BC, Schlittler DL, Glickman NW, Glickman LT, Waters DJ. Endogenous gonadal hormone exposure and bone sarcoma risk. Cancer Epidemiology, Biomarkers, and Prevention 2002;11:1434-40.) The neutered animals in this study (especially the spayed females) also lived longer than the intact animals, which may have contributed to an increased incidence of cancer in the neutered group.
These results haven’t been replicated, and while neutering may increase the risk of OSA in some breeds when performed at some time point, the general relationship isn’t clear, and this may not matter for most dogs if overall neutered animals still live longer than intact animals. Again, the details matter, and broad generalizations are not supported by the limited data. Likely, the risk/benefit balance of neutering will depend a lot on breed and timing and other factors. The Waters’ findings haven’t been replicated and, in fact, a recently published review including over 850 Rottweilers found no effect of neutering at any age on the incidence of cancer, including OSA.
I’m so confused. We have two Shepherd/Husky girls. They’re almost 2 years old and intact. I’ve read that Shepherds have a higher risk for developing a certain cancer (hemangiosarcoma) and that spaying them will increase the risk. On the other hand, spaying them will decrease the risk of developing other cancers and possibly increase their life span. What should we do? Should we get them fixed?
In females, the risk of pyometra and mammary cancer is very high, and overall neutering would be of more benefit than remaining intact. It might increase the risk of hemangiosarcoma, but it would decrease the risk of breast cancer and uterine infection, and overall the benefit outweighs the risk. But remember, this is for a population of dogs. No matter which you do, some dogs will get hemangisarcoma whether neutered or not, and a very few will get breast cancer even if spayed. There is no perfect answer for every dog; we are playing the odds, and they are in favor of neutering for most females.
Look up OSS.. ovarian sparing spay… It is basically a hysterectomy.. and they keep the ovaries… We did this for our female German shepherd… Occasionally drops of blood (lot less than non spayed females)..and still goes into heat but cannot get pregnant and no pyometra.. because uterus is filled removed). Just look out for mammary tumors… So reduces acl tears.. and hopefully prevents hip dysplasia because she kept her ovaries. Good luck
Mammary cancer risk is the same as intact. Pyometra risk depends on how completely the uterus is removed. It is routine to remove the uterus proximal to the cervix with a standard spay since there is no risk of a stump pyometra if the ovaries are taken out. Vets performing an OSS need to also change this practice to remove the cervix or a pyometra can easily still occur. There is slightly greater risk in taking the cervix since it is closer to the vagina and the entry of the urinary tract, but it can be safely done.
The problem is that there is still no comparative research evidence showing a net health benefit to this procedure. All the risks and benefits of neutering vs leaving a pet intact are essentially the same except for removing the potential for reproduction and reducing pyometra risk. Whether or not it reduces CCL disease, for example, depends on breed and age at neutering. Hip dysplasia is also complex, and the association with neutering is dependent on breed and body weight and early nutrition, so neutering is only one of many relevant variables.
I have a yorkie/ shih zsu that’s 2. 5 years old , I don’t see the benefits of neutering at this point, I feel surgery is just risking his life . I think he can be trained not to mark with consistency ? He is so passive already, I don’t think the health benefits of N out way the future complications they can have. Do you agree?
Basically I agree, though of course it’s never that simple.
It’s pretty much impossible to predict the health outcome of an individual dog, and remember neutering only shifts risks up or down in concert with a million other risk factors: it’s unlikely to be the one thing that definitively causes or prevents most problems. If your dog is one of the rare ones that gets a testicular tumor one day, for example, then obviously neutering would have prevented that for him, regardless of the overall effects of neutering in a population of dogs.
That said, there’s no strong evidence that neutering is likely to improve the health of an adult small-breed dog, so I don’t see a compelling reason to do so if there isn’t a specific problem to be fixed (like prostate disease or inter dog aggression, for example).
Thank you for your opinion, 4 Vets told me he needs to be Neutered until this one Vet said why would you risk his life to neuter him at this stage. That had me researching for answers. He also said Neutering at this stage won’t change his marking habits. I really believe he will be Healthier intact.
Thanks again, I feel relieved. 🙂